Ardour - - A multichannel digital audio workstation for Linux.
EasyTAG Project - - A GTK+ GUI program for quickly and easily editing info tags on MP3 music files.
mbux - - An open-source mp3, ogg, and flac music box designed for use at public places, so that users may only queue songs, not remove them. Features, screenshots, documentation, and download.
Moe Music - - Moe Music is a PHP-based database for music powered by MySQL. It allows users to add music to a database for use in a LAN party.