Audacity is a cross-platform multitrack audio editor. It allows you to record sounds directly or to import Ogg, WAV, AIFF, AU, IRCAM, or MP3 files. It features a few simple effects, all of the editing features you should need, and unlimited undo. The audio I/O uses PortAudio, which fully supports OSS, Mac OS X CoreAudio, and Windows WMME, and can be compiled with support for ALSA and Jack.
Quod Libet is a music library management program. Rather than categorize songs by genre, artist, and album, it lets you search and display them however you want. It supports regexp-based searches, album cover display, tag editing, ReplayGain, multimedia keys, and an OSD. Also included is Ex Falso, a tag editor that has the same editing features found in Quod Libet, but does not play audio files.
Music Manager is a Konqueror plugin that lets you standardize the filenames of your music files, guess information and set ID3 tags from the file's name (this can be done to several files in one shot), rename many selected files based on their ID3 tags, set ID3 tags in mass for selected files with options for copying ID3s from other files and leaving some ID3 fields untouched, rename _ to space and vice versa, create HTML and text indexes of your collections (including total playing time, etc., configurable through templates), create nice CD covers with full listings of your music files (also configurable through templates), and organize your music collection to create a CD.
SimPlEdi is a Web-based editor for MP3 playlists (M3U) which are used in popular music players like Winamp or XMMS. The file locations are stored relative to the playlist location, which makes it possible to use the generated lists on changing environments such as mounted network drives or CDROMs.
KPlaylistCreator is a jukebox for KDE. It scans for MP3 and Ogg Vorbis files, located in various directories, creates a unique tree view with genre, artist, album, and song title information, features a user rates mechanism, a user playlist manager, and a wizard playlist creator, edits tags for both MP3 (ID3 v2) and Ogg Vorbis files, checks directories for new and missing files automatically, sends playlists to a directory, XMMS, or to K3B, displays and sets the album art of MP3 files, creates playlists from a virtual library, and includes popup windows to indicate change of song.