Musicbrainz Picard is a digital audio tagging program developed to accompany the Musicbrainz database. In the same spirit as the open-source software movement, the open data movement holds that certain bodies of information should be available to all. Entries in the Musicbrainz database are added and maintained by volunteers (and are surprisingly thorough!). Distinction is even made among releases of an album in different countries and with/without bonus tracks.
The curation effort has expanded to include cover art and acoustic fingerprints. (An acoustic fingerprint is a digital summary of an audio signal — the type of technology used by apps like Shazam.) Audio files track_01.mp3, track_02.mp3, etc. are mapped to their respective chunks of metadata from the database. Picard then outputs the files fully tagged.