Short answers, pulled from the story.
MusicBrainz is a collaborative music database run by the MetaBrainz Foundation, a non-profit based in San Luis Obispo, California. It was created by Robert Kaye, who turned the project over to the Foundation in December 2004. The database holds information on over 2.8 million artists, 5.4 million releases, and 38.7 million recordings.
MusicBrainz was founded in direct response to restrictions placed on the Compact Disc Database (CDDB), which software applications used to look up audio CD information over the internet. The project aimed to build a freely accessible, community-maintained alternative that no single company could restrict.
MusicBrainz uses the Chromaprint algorithm, started in February 2010 by contributor Lukáš Lalinský, to identify recordings by their acoustic fingerprint. Chromaprint analyzes the first two minutes of a track, detecting strength across 12 pitch classes eight times per second, then compresses the result into a fingerprint used by the AcoustID service for matching.
MusicBrainz's core data has been dedicated to the worldwide public domain since 2003 under the Creative Commons Zero 1.0 Universal legal tool. User-contributed content and the live data feed are published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. The client library libmusicbrainz is licensed under the GNU Lesser General Public License 2.1, which permits use by proprietary software.
The Cover Art Archive is a joint project between MusicBrainz and the Internet Archive, launched in 2012. Internet Archive provides storage, bandwidth, and legal protection, while MusicBrainz manages the metadata and public API access. Over six million images are stored in the archive.
MusicBrainz Picard is a free, open-source application that identifies digital audio files and compact discs by comparing their metadata or acoustic fingerprints against the MusicBrainz database. It then writes detailed tags to the files, including artist name, album title, record label, and release date, across formats such as MP3, FLAC, AAC, and Ogg Vorbis.