MusicBrainz is a community-maintained open source music encyclopedia that collects music metadata and makes it available to the public.
MusicBrainz Picard is an open-source software application for identifying, tagging, and organizing digital audio recordings.
CritiqueBrainz fills the gap between music and book critics and raw data by providing a platform created for the sole purpose of Creative Commons licensed reviews.
BookBrainz is an online encyclopedia containing information about published literature. Its aim is to collect and store data about every publication ever written.
ListenBrainz is an open source music website that allows users to import their listen history. One of the goals is for this data to be used for building open music recommendation systems.
MessyBrainz identifies unclean metadata, and where possible, links it to stable MusicBrainz identifiers. MessyBrainz was used for AcousticBrainz and is still being used in ListenBrainz.