The Musixmatch Python SDK by Luca De Vitis allows to interact with the API to access catalogs of lyrics, that aim to be useful to implement into music applications. Resources include a quick start guide, installation, documentation, and unit testing.
Seevl is a new kind of music discovery engine. It allows you to find how artists are similar to each other and which artists are most similar to each other, among other things. It also allows you to comment on the notes about artists within the database. This is all well and good, but better yet, it has the Seevl API, allowing developers to integrate Seevi into their own applications.
Spotify has just added the Spotify Web API to Mashape, a popular marketplace where cloud APIs can be distributed, monetized, managed and consumed. Developers can use the Spotify API to search and display data such as albums, artists and music tracks from Spotify's vast music database.
Gracenote "touches hundreds of millions of music fans and TV viewers everyday. The Gracenote database is the largest source of music and video metadata on the planet, featuring descriptions of more than 130 million tracks and TV listings for 28 countries." Recently, Gracenote launched a developer program that opened its Gracenote API to the developer community. The API delivers Gracenote's rich music metadata to any connected app.