SQL Tagger reads the tags of audio files from a directory, loads them into a temporary SQLite database, accepts SQL queries to modify this database, then saves any changes back to the audio files. It's useful for performing complex updates that would be difficult or tedious with conventional taggers. It's a complement to conventional taggers, not a replacement.
Flac2All is a multi-threaded script that will convert your collection of FLAC files into either Ogg Vorbis, MP3 (with the Lame encoder), or FLAC, complete with any tags and identical file/folder structure. The script has been stable for about a year now, and it has been known to saturate 8-core machines with parallel conversions. It is useful for people with with large FLAC collections who also want a lossy version for portable media players. If wanted, the script can perform updates by skipping already converted files. It has only been tested on Linux, but it should work without alteration on the other Unix systems with bash and the required dependencies.
puddletag is a tag editor for Linux loosely based on mp3tag. It uses a table layout so that all the tags you want to edit by hand are visible and easily editable. puddletag excels at automating repetitive tasks like extracting tag information from filenames, tagging files from a text file or the clipboard, renaming or moving files and folders based on tags by using patterns, and manipulating tags using actions and regular expressions. Supported formats include id3v1, id3v2 (.mp3), AAC (.m4a), VorbisComments (.ogg, .flac), and APEv2 (.ape). Much of mp3tag's functionality has been replicated with added enhancements and tweaks.
Peyote is an audio player with a friendly MC-like interface. It is designed specifically to work easily with cue sheets. It plays wv (wavepack), WAV, FLAC, APE, Ogg, WMA, and MP3 formats. It supports ID3v2, APEv2, FLAC, and Vorbis tags; multiple playlists; and tabs. It can copy, move, remove, and rename files.
Flac-utils is a toolkit for managing FLAC files. Its primary usage is syncing metadata between sets of FLAC files. Flac-utils also provides a Python module called flac_compare that can be used separately. The utilitiy consist of three tools: flac-sync, which syncs a file tree of FLAC comments for files with the same audio-part; flac-diff, which compares two FLAC files' metadata information and shows the differences; and flac-add-picture, which adds album cover art to the files using Amazon.