AlsaPlayer: PCM player written for ALSA driver and library, supports other outputs like OSS and esd. Plug-in interface.
Audio File Library: An API for accessing a variety of audio file formats.
Aumix: Adjusts an audio mixer. X and ncurses interfaces.
Baudline Signal Analyzer: Realtime signal analysis and spectrum analyzer tool.
BEAST/BSE: GTK+/GNOME based front-end to BSE framework to simulate audio synthesis and tracking composition.
Cdgtools: Suite of tools for handling CD+G karaoke disks and files.
CoverViewer XMMS Plugin: Displays covers or images related to songs. Internet cover retrieval facility. Handles tagged files, CDs, and streams.
Dir2ogg: Python script that converts MP3, WAV, and M4A files to Ogg format.
Ecasound: Audio software for Unix.
Geoff and Dave's Audio Mixer: A digital audio mixing package.
GLAME: Free and extensible Linux/Unix audio editor. GNU licence.
GNOMAD: GTK+ client program for the NOMAD Jukebox, using libnjb and id3lib to handle communications and ID3 tagging.
Gnome Wave Cleaner: An audio cleanup tool for GNOME. Handles WAV, MP3, and Ogg.
GramoFile: Assists in moving gramophone records onto CDs. Filters out hiss and pops.
Grip: Cd-player and cd-ripper. It also provides an automated frontend for MP3 and other audio format encoders.
IMMS: Intelligent Multimedia Management System: Playlist plug-in for XMMS that tracks the user's listening patterns and dynamically adapts to suit tastes.
KGuitune: A program for tuning guitars and other instruments that is available for download.
Lilypond: Creates beautiful music notation from text input. Outputs Postscript, SVG or MIDI files. GNU license.
Linux Sampler Project: Audio sampler with features similar to hardware samplers. Offers speed, high audio quality rates, supports common sample library formats.
Matti Koskinen Software: Programs including a de-noiser, MIDI generation from fractals, sound creation from gifs.
Mixxx: Open source DJ mixer.
MusE: MIDI/Audio sequencer with recording and editing capabilities.
Orpheus: Text and window mode audio player for CDs and MP3 with CDDB interface.
Philip's Music Writer: A music typesetter. Input is a plain text file, output is in PostScript.
PyKaraoke: CDG/MP3+G karaoke player. Can search inside Zip files.
Rosegarden: MIDI sequencer and notation editor for Unix-like systems.
SndStretch: Plug-in for XMMS to adjust pitch and tempo of a sound.
Sound Processing Kit: An object-oriented class library for audio signal processing.
SoundTracker: MOD tracker for X, similar to FastTracker. Includes a sample recorder and editor.
Spatializer StreamFX: Enhancement software for Linux XMMS Player. 3D stereo, dynamic bass.
The TAON Project: A sound editor for Linux.
TiMidity++: MIDI player, converter to wav. Uses Gravis compatible patches and can play these through soundcards lacking their own patches.
XMMS-SID SIDplay Plugin: Plug-in for playing Commodore 64 music (SID tunes) with XMMS. Requires libSIDPlay library (link given).
xmp: Extended Module Player: Open source (GNU GPL) portable module player for Unix or Win32.
Zero Tolerance's Cue Creator: A small Perl script that allows you to create CUE and MP3/OGG/WAV-files from audio CD's.
ZynAddSubFX: Synthesizer with two engines, realtime polyphonic, Midi support, microtonal capability, effects.