The MusicBrainz C/C++ Library by MusicBrainz is a client cover art archive library for developers. Using this library, developers can add cover art capabilities to their applications. The MusicBrainz database contains a huge amount of music metadata, which is maintained by the MusicBrainz community.
The University of Michigan Medical School created the Vaccine Investigation and Online Information Network (VIOLIN) because the vaccine research field lacked a web-based central repository where researchers could easily retrieve the vast amount of data underlying hundreds of years of research. Not only has VIOLIN provided the online database, the database is easily accessible via the VIOLIN API.
The Punkrock.org API uses POST and GET calls that allow a user of your app to access their own user info on Punkrock.org, including friends, mail, notifications and allows them to upload photos. Requesting an API key is required for access to services.