Cd-player and cd-ripper. It also provides an automated frontend for MP3 and other audio format encoders.

GTK+/GNOME based front-end to BSE framework to simulate audio synthesis and tracking composition.

PCM player written for ALSA driver and library, supports other outputs like OSS and esd. Plug-in interface.

MIDI sequencer and notation editor for Unix-like systems.

Creates beautiful music notation from text input. Outputs Postscript, SVG or MIDI files. GNU license.

Open source (GNU GPL) portable module player for Unix or Win32.

An API for accessing a variety of audio file formats.

MOD tracker for X, similar to FastTracker. Includes a sample recorder and editor.

Open source DJ mixer.

MIDI player, converter to wav. Uses Gravis compatible patches and can play these through soundcards lacking their own patches.