Notes.Studio for linux

Digital Audio Editors
Ardour
Audacity

Slab - SLab Direct to Disk Recording Studio.
MiXViews
Snd - Snd can accomodate any number of sounds at once, each with any number of channels.
SoX: Sound eXchange - SoX is a sound file format converter for Unix. It's the swiss army knife of sound tools.
Broadcast - A multi-tracking digital audio editing program

Aglaophone - Real time processing and analysis of audio signals
ecasound

Freebob
fmit instrument tuner

GWC

jaaa
japa
JAMin

Lilypond
LinuxSampler

Meterbridge

Rosegarden
Rezound

Sweep
Sonic Visualiser

Time Machine

muse Qt-based midi/audio sequencer

Tools
vkeybd virtual midi keyboard

Synthesizer Emulator
amSynth
mx44

Bristol

Fluids
ynth
QSynth
Specimen
Hydrogen
Aeolus
Hexter
WhySynth
Sineshaper
Nekobee

Om Synth
AMS
ZynAddSubFX
MMS
Creox

Effects and Loops
Ecamegapedal
jack-rack
Freqtweak
TerminatorX
FreeWheeling
SooperLooper

Multimedia players
XMMS
Kaffeine media player
XJadeo


XMCD

DVD/CD burning
K3B
KAudioCreator
Arson

VST plugins

Video/DVD Players

Mplayer
XAnim
Xine
Ogle DVD
VLC

MIDI Tools and Players
Rosegarden Suite - The Rosegarden suite is a free musical notation editing and sequencing system for a variety of machines
CSound - Csound is a sound and music synthesis system
CMIX - CMIX is a computer music "language" designed to create and manipulate soundfiles. It is somewhat similar to Csound.
TiMidity - TiMidity is a MIDI to WAVE converter (MIDI renderer)
Keykit
Direct Music
aRTs - aRts simulates a complete "modular analog synthesizer"

Bristol - Synthesiser emulation package

KMid
Tclmidi

Mixer Applets
Smix
Mix2000 Works with Broadcast 2.1
aumix
Xmmix
KMix

Trackers/MOD Players
Funktraker
SoundTracker - SoundTracker is a pattern-oriented music editor
XMP
XGMOD
NSPmod
MikMod

Streaming Audio

CD\DVD Tools

dvd95: convert DVD9 to DVD5