There's of lot of behind-the-scenes work using linked data and cultural heritage APIs.  When data is open, as well as structured, people outside the organisation can make cool stuff.  Here's a selection of sites, apps and hacks that help demonstrate the value of linked open cultural data.  If you've made something cool or useful, don't be shy - add it to the list!

• Southern Mosaic by Aditya Jain, from the folk song collections of the Library of Congress
• When art meets big data: Analyzing 200,000 items from The Met collection in BigQuery - using the Met's collections to demonstrate 'big' data and machine learning techniques with metadata and images of artworks
• Visual Timeline Experiment by agency Askew Brook with records from the Harvard Art Museum
• Hackathon with records from the Slovak National Gallery and the Norwegian Nasjonal Museet
• Simple but effective - WCMA records 'mapped by brightness & hue'
• 'Ensuring the unexpected' is a blog post describing how data in the SOCH (Swedish Open Cultural Heritage) / K-samsök web service has been used
• America’s Public Bible uses newspapers from Chronicling America via the Chronicling America API. The newspaper metadata comes from the newspaper metadata API. The OCR plain text of the newspaper pages was downloaded via the OCR Bulk Data API.
• A nonparametric view of the civilizing process in London's Old Bailey by Jasper Mackenzie, Raazesh Sainudiin, James Smithies and Heather Wolffram (PDF) - an academic article on a project that ran statistical analysis of the Proceedings of the Old Bailey Online. See also this impressive list of 'Projects Which Have Used Old Bailey Online Data'.
• How We Learned to Stop Worrying and Love Open Data: A Case Study in the Harvard Art Museums' API by Andrea Ledesma & Leah Burgin
• R Client for Scraping Museum Metadata - currently works with the Met and others
• New York Public Library (NYPL) has created 'Public Domain Remixes' to inspire potential users of their public domain collections
• A visualisation project based on MoMA data: 120kMoMA - A data visualization study of The Museum of Modern Art collection dataset of 123,919 records by Helen D. Wall.
• Helen Wall also created '120kMoMA peak years — A data visualization study of years information in The Museum of Modern Art Collection dataset'
• The British Library's Labs Awards 2015 winners have been posting about how their entries used the digital collections of the British Library. A particular highlight is Mario Klingemann's work with classifying images on Flickr Commson: Creative/Artistic category Award winning project
• The British Library Labs Competition 2015 award winners are using digital collections in interesting ways
• The Netherlands Institute for Sound and Vision (Beeld en Geluid) say 'be inspired by what others have made with our datasets and code'.
• Geoff Hinchcliffe's interface for Tate's open collections data
• A Nerd's Guide To The 2,229 Paintings At MoMA by Oliver Roeder for fivethirtyeight
• Photomediations: An Open Book uses content from Europeana, Wikipedia Commons, Flickr Commons for an updated, digital version of a coffee-table book.
• Gutenberg Authors 'connects Project Gutenberg authors to DBpedia metadata allowing you to find books based on the author’s information. For example answering questions like: “Books written by Nobel Laureates”. Created by Matt Miller.
• DigitalNZ has published a page which showcases the various uses of the DigitalNZ API: http://www.digitalnz.org/about/digitalnz-api-in-use 
• A report on the EEBO-TCP Hackathon by Dan Q (that's Early English Books Online Text Creation Partnership, more on the hackfest and sources here)
• The colors of paintings: Blue is the new orange provides code and explanation for a visualisation 'of the change in colors of paintings over time'; the paintings used come from BBC/PCF's Your Paintings
• Museum of New Zealand Te Papa Tongarewa released open access high resolution downloadable images from their Collections Online in 2014. They blogged about the statistics and examples of use in April 2015. Read the blog here http://blog.tepapa.govt.nz/2015/04/10/reusing-te-papas-collections-images-by-the-numbers/, and access the data from the Te Papa github repository here https://github.com/te-papa/image-downloads-stats. 
• Rob Hudson, Associate Archivist at Carnegie Hall, has written a series of posts on Visualizing Cultural Heritage: Linked Open Data and the Carnegie Hall Archives p. 1 and Visualizing Cultural Heritage: Linked Open Data and the Carnegie Hall Archives p. 2 (on using Apache Marmotta, RelFinder and LodLive). They're particularly interesting as Rob isn't a programmer but has managed to get some interesting work going.
• In The API at the center of the museum, Cooper Hewitt explain how their API supports and underlies the work of the museum
• 'Active shelves' at the Oslo Public Library 
• Mapping Artistic Attention in Amsterdam, 1550-1750 by Matthew Lincoln draws on data from the Rijksmuseum API to examine how representations of locations in Amsterdam shifted as the city expanded over two centuries.

• The Muninn Project is working on Retrieving Historical Art from the Rijksmuseum

• A surprising use of Trove's music 'Recently a Trove user, plumber, contacted us to ask whether he was doing the right thing by adding comments to sheet music items in Trove, which included links to YouTube videos and SoundCloud files. ... plumber was not only adding links to YouTube videos and SoundCloud files, they were links to files which had the audio of the sheet music found in Trove as created by plumber!'

• Some great projects are listed at 'Art Bytes: 14 projects from the second Walters Art Museum hackathon' - not just the usual hackday stuff!

•  SPARQL for humanists by Matthew Lincoln shows how you can use the Europeana SPARQL endpoint: 'Unfortunately, many tutorials on SPARQL use extremely simplified data models that don’t resemble the datasets you’ll find in Europeana or other institutions like the British Museum. This tutorial tries to give a crash course on SPARQL using a dataset that a humanist might actually find in the wilds of the Internet.'

• Not really an API story but still lovely uses of open cultural data. The Public Catalogue Foundation reports 'The anonymous paintings brought to light by the PCF have already been a fertile field for new attributions. More than once the experts in the BBC television series Fake or Fortune have sought a lead for their quest on the Your Paintings database, while a Facebook group of art historians under the generic name ’Le Connoisseur‘ have developed an amusing parlour game for guessing the authorship of old master and modern paintings, with Your Paintings prominent among their sources.'

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• In The scholarly impact of opening up content, Katharine Lindsay lists some scholarly works and media that have used the open content they published about the First World War.

• Yvonne Perkins has written a very user-friendly guide to using the Trove API which is also a good introduction to APIs, An Introduction to the Trove API.

• applying digital humanities approaches to museum collection data by desi gonzalez looks at New York's Museum of Modern Art data

• Forte: the National Library of Australia’s sheet music collection iPad app by Paul Hagon. 'We didn’t quite know what would happen with the dataset & how it would end up being used in the competition. Unfortunately it didn’t really get used in a major way in any of the entries and the dataset sat there gathering electronic dust. Nearly 12 months later, totally out of the blue, someone walked into the reading rooms at the library, approached the person on the desk (who, as luck would have it was Sarah who was the project manager for our iPhone catalogue app), introduced themselves and said “Hi, my name is Jake & I’ve built this” & showed off what was the first prototype of what went on to become Forte.''...three really important lessons to come out of this:

1. Make your data available.
2. Don’t expect things to happen immediately
3. If you can, guide the developer to help them fine tune their product & give them insight into the intricacies of the data.'

• A post on visualising 'The Tate Collection on GitHub' by Florian Kräutli, another on Exploring The Tate Collection by Eric Drass at Shardcore and one with sample code for loading their JSON data from github into MongoDB (Exploring the Tate Collection Metadata) by Rob Myer. And another on The Dimensions of Art ('the dimensions of every piece of art that the Tate owns') by James Davenport. Further examples of the Tate Collection in use are collected on Tate's Collection GitHub page.
• The Web Data Inspector (BETA) isn't made with GLAM APIs but it'll help you explore their data. 'The Web Data Inspector is a tool to Visualize and Validate the structured data content available at a given web location (URL). The Web Data Inspector can be used to visualize and validate: RDF files; HTML pages embedding microformats; XHTML pages embedding RDFa'.
• Serendip-o-matic: let your sources surprise you is a "serendipity engine" that parses text for keywords and queries various aggregators for results. About page and information on adding your sources.
• Digital Public Library of America Autumn 2012 'Appfest' results including useful code libraries and their Summer 2011 Beta Sprint results
• Open Context uses linked data to link their archaeological research data and archives records to the British Museum's CIDOC records
• A pilot study 'STELLAR: Semantic Technologies and Linked Data' including work with the National Museum Wales and Science Museum group (UK) data
• Discover French Monuments through Open Data! "a search-based application to find historical monuments: with full text search; in a given region, department or city; by type of monument: church, castle, statue, industrial site; by historical period: prehistoric, medieval, Renaissance etc.; by type of owner: person or private corporation, municipality, state…with all possible combination of these criteria as very easy to use “faceted search” and the search itself (in French): http://labs.antidot.net/search?afs:service=50005 
• Culture Hack North hacks listed on their site and as reported in the Guardian:
• Whitworth's Landscape Paintings Mapped which used data from the Whitworth Art Gallery, Manchester.
• Film Finder which used data from Cornerhouse, Manchester
• Name That Train which used data from the National Rail Museum to make a small train game where users have to identify a train at York railway museum by a very small picture.
• Trains Near Me which used data from the National Rail Museum.
• Smooth operettas which used data from Opera North.
• Colour Tone data from Whitworth Art Gallery and Manchester Museum.
• Round the corner reviews, trailers and descriptions of films at Cornerhouse.
• InformedApp an app which helps people gen up on cultural information from any dataset source.
• Shared History – Common Culture data from CultureGrid API.
• Consider the library described as gentle reminder that books available online are often available from the library.
• KhaKauRe a graph, wikipedia like initiative which neatly managed to use data from almost all of the participating organisations.
• The Dutch are at it again! There's an English-language overview of how they encouraged re-use and what was made at 'Open Culture Data: Creative Re-use of GLAM Data'. The 2012 Open Cultuur Data Awards, page 2 attracted 27 entries using 35 datasets. The winners are Muse App (gold, make new pictures from images cut out from paintings): http://www.museapp.org Histagram (silver, make postcards from historic images): http://www.frontwise.nl/lab/histagram/ SimMuseum (bronze, play at being a museum director): http://simmuseum.haykranen.nl/ Tijdbalk.nl (Nationaal Archief prize): http://tijdbalk.nl/
• The Rijksmuseum API page lists projects built with their API, including some that link content to Twitter, Spotify, facial recognition, quiz apps, themed browsers and much more.
• Apparently the MarineLives project (see also http://www.historytoday.com/colin-greenstreet/crest-wave) was inspired by The National Archives hackday
• What is this?  is a really simple site that asks you to give one word to describe a random object, based on the CSV-downloadable collections of the Science Museum Group (UK). Source code and credit: https://github.com/frankieroberto/things 
• Europeana Labs Apps Showcase - projects implementing the Europeana API, including Inventing Europe, Digital Humanities Observatory, Europeana eCloud, Dutch Museum of National History, National Library of Ireland catalogue widget, VuFind Europeana search results recommendation module, Royal Museum for Central Africa search and Serendi-o-matic
• eight projects from the first-ever Walters Art Museum hackathon
• early Europeana Hack4Europe 2012 results and a list of Europeana Hackathons winning prototypes from 2011, 2012 plus a post by Uldis Bojars on a hack built in Riga: 'Europ.in is a visually-engaging web application for exploring Europeana content' - inspired by Pinterest.
• ManyEyes visualisations of Cooper-Hewitt and NMSI/Science Museum Group data by bartdavis and this Cooper-Hewitt Labs blog post about this use of their data at http://labs.cooperhewitt.org/2012/collection-data-eyes/. See also Hacking on Cooper-Hewitt's data release at THATCamp, Or, How to get me to work for free (*).
• Australian GovHack winners in the cultural heritage/digital humanities section, awarded by the National Archives of Australia. Best use of the Archives data set: History in ACTION by team History in ACTION - A website which gives Canberrans and visitors the opportunity to create their own personalised bus tour exploring Canberra’s rich history; Photo Search by team Double Rainbows - These images are more than just pretty pictures; they reveal to us our history and identity; where we come from and what makes us Australian. Discover this country through its’ history and through these awesome archive of images.  Best overall: A Day in the Life by team The Outsiders – A Day in the Life aims to provide a personal connection with the archives and statistical data.
• Search the UK's CultureGrid by colour with CultureGridNE:colourAPP
• MuseumFinland - Finnish Museums on the Semantic Web. The site dates back to 2004, and information in English is available at http://www.seco.tkk.fi/applications/museumfinland/.They're also working on a Linked Data solution, more at http://www.seco.tkk.fi/projects/ldf/.
• It's worth keeping an eye on ResearchSpace, a project from the British Museum 'aimed at supporting collaborative internet research, information sharing and web applications for the cultural heritage scholarly community'.
• Results of The National Archives’ first hack day. Resources used include wartime Cabinet Papers (UK WAR CABINET January 1940 – July 1941), “Ancient Correspondence”, Medieval lenders and debtors, Olympic data... The National Archives' blog has write-ups including 'BT 31 – The Birth of Industries and #hackon12: We came, we saw, we didn’t sleep much
• Cultural apps from the 'Apps for the Netherlands competition': http://www.opencultuurdata.nl/2012/01/apps4nl-overzicht-van-open-cultuur-data-demos/ (Google Translate version in English: http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=www.opencultuurdata.nl%2F%3Fp%3D569&act=url).  There's a summary at http://openglam.org/2012/03/12/open-cultural-data-success-of-cultural-apps-in-the-apps-for-the-netherlands-competition/ "The app that went home with the overall gold prize was ‘Vistory‘, built and designed by Glimworm IT. Vistory combines history and videos from the Open Images dataset by using a smart phone’s geo-location technology. By freezing a frame, the user can recognize a location and take a photo using an overlay “reverse augmented reality” function of the app. When the picture is taken, the video is tagged with the exact geo-location. Also, the specific time signature on the video is tagged with the photo of how the scene looks, creating a “then and now” effect.".
• Brooklyn Museum maintains an Application Gallery published on our website that details each application as it's developed and where to find it.   You can also subscribe to our API News area via RSS and applications are announced there as well.
• Brooklyn Museum also highlights more in-depth information about applications and interviews with Developers in the API tag of our blog and this tag is also available via RSS.
• Brooklyn Museum API: the iPhone app
• From their interview with the developer: "In my mind, there are few things that inspire people to learn like museums and the web do. ... Once I saw what the [Brooklyn Museum] API allowed, it seemed like an opportunity to create something that people would enjoy. The key to invention in this field is to build things that people don’t realize they will use.
• Because all the content is pulled from the API, it is a very lightweight app that will be convenient for users to update. When the iPhone 3.0 OS goes public in June, we are planning a much more exciting geotagging experience, because the built-in mapping is making a great leap forward. Also we are interested in allowing users to tag items in the collection, expand the browsing options, etc. The main point I want to emphasize is that this is only the beginning, and we are planning to expand the application as the API evolves."
• Brooklyn Museum API: Collections iPad App "Our collection data can now be found on the iPad courtesy of Wayne Bishop and his Art Collections app. ... 'Our application, named Art Collections, is a free app that allows users to browse art, photographs, antiques and other content from the museum.  The application provides access to over 25,000 pieces and was built specifically for the iPad (and iPad 2) because the large touchscreen allows users to scan, zoom, and touch the art.  The app is available in the iTunes App Store.'"
• Museum Pipes has some great examples of the possibilities available to non-programmers and a GUI interface.
• Museum Victoria (Australia) has discussed how they could use APIs for their community collections project, Collectish in this project blog post, World Collections: "The fundamental problem with trying to create a mashup with Museum collections is that there are very few that have exposed their collection database via an API or an OpenSearch feed. However quite a few have built some sort of mechanism to browse their collections online which means that we can query them indirectly using the Google API".
• Powerhouse Museum collection data was used in several of the Mashup Australia contest entries. Most notably one of the winning entires built a new in-gallery collection browser. More at http://www.powerhousemuseum.com/dmsblog/index.php/2010/11/11/quick-interview-with-amped-powerhouse-api-winners-andrea-lau-jack-zhao/.
• Powerhouse Museum data was also used for museum metadata games (more info at http://www.powerhousemuseum.com/dmsblog/index.php/2011/01/03/interview-with-mia-ridge-on-museum-metadata-games/) and for 'Mashificator' (more info at http://www.powerhousemuseum.com/dmsblog/index.php/2010/11/04/making-use-of-the-powerhouse-museum-api-interview-with-jeremy-ottevanger/).
• Science Museum, National Media Museum, National Railway Museum (UK) released collections data as CSV. Examples are being listed at Virtual Repatriation and the Application Programming Interface: From the Smithsonian Institution’s MacFarlane Collection to “Inuvialuit Living History” (Museums and the Web)
• From Sharing cultural heritage the linked open data way: why you should sign up: "Three apps made with cultural data won prizes. In the category Education, the Rijksmonumenten.info (http://rijksmonumenten.info/) mobile app by ab-c media (http://www.ab-c.nl/) containing (location-based) information on Holland’s 61,000 heritage sites won. ConnectedCollection (http://www.opencultuurdata.nl/?p=583) from Cit (http://www.go2cit.nl/) won an encouragement prize to further develop their tool that allows cultural institutions to add a button on their collection websites showing related objects from other heritage institutions when clicked. The app that went home with the overall gold prize was ‘Vistory‘ (http://www.vistory.nl/what-is-vistory.shtml), built and designed by Glimworm IT (http://www.glimworm.com/). Vistory combines history and videos from the Open Images dataset (http://www.opencultuurdata.nl/?incsub_wiki=nederlands-instituut-voor-bee...) provided by Sound and Vision by using a smart phone’s geo-location technology on a certain spot. By freezing a frame, the user can recognize a location and take a photo over it using a "reverse augmented reality" function with the app and the camera on a smart phone. When a picture is taken, the video is tagged with a geo-location so others can find it more easily. Also, the specific time signature on the video will be tagged with the photo of how the scene looks, creating a "then and now" effect. A demo of the Vistory app can be found at http://youtu.be/MXt4ExebHsA"
  
• Crotos is a search and display engine for visual artworks based on Wikidata and using Wikimedia Commons files, with Wikidata Query, Wikidata API and Wikimedia Commons API. Formerly based on data extracted from DBpedia, the project won in 2014 at Sémanticpédia Contest the prize "Promotion of cultural and linguistic data". 
• On This Day - explore content by date in history, brought together from an ever growing range of sources including Europeana, Flickr Commons, Imperial War Museum, National Maritime Museum 
• Europeana Colour Explorer - demonstrator for the new (as of late 2015) Europeana colour indexing (also available just for Europeana Fashion images)
• This Stone is a narrative game about commissioning a runestone in 11th century Uppland, Sweden; it uses the SOCH API to find images of real runestones to match the choices made by the player. 
• Kyrksök ("Church Search") combines data from SOCH, Wikidata, and WikiMedia Commons to create a mobile web app about Swedish churches. 
• Pastpin is a google images for historical photos. It also encourages users to contribute new metadata to improve the individual record. 
• PostcardTree is a search engine for handwritten postcards.  
• Automated image analysis with IIIF A search interface of the Swedish Nationalmuseum's collection using several Image recognition tools and IIIF images. By Cogapp (See blogpost).
• OpenCCTVdragon Another tool using the Swedish Nationalmuseum's collection to provide a 'control room' and linked 'viewers': see what the viewers are viewing. By Cogapp (See blogpost).
• Trading Card Explorer A Google Cardboard explorer of vintage trading cards from the Boston Public Library served via IIIF. By Cogapp.