picard.musicbrainz.org
MusicBrainz Picard is a cross-platform music tagger written in Python and powered by the MusicBrainz database. It supports formats such as MP3, FLAC, OGG, M4A, WMA and WAV, uses AcoustID audio fingerprints, and can look up entire CDs. It is open source under GPL 2.0 or later and supports scripting and plugins.