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Recording and editing
The following packages are digital audio editors:

ACID XPress 5.0 (Windows)
Ardour, a multi-track audio recorder (DAW) (Linux, Macintosh)
Audacity, multi-track audio recorder/editor (Linux, Macintosh, Windows)
Audiobook Cutter Free Edition, MP3 audiobook splitter (Windows)
Ecasound, audio recorder (Linux, Macintosh)
Freecycle, beat slicer (Linux)
Jokosher, a multi-track audio editor (Linux)
Kristal is a digital audio editor, multi-track recorder and sound mixer (Windows)
LMMS, a powerful musical studio intended as a replacement for Cubase-like software (DAW) (Linux)
Mp3DirectCut, edit MP3 files without decoding or re-encoding them. (Windows)
Mp3splt, splits MP3 and Vorbis files without decoding (see mp3splt-gtk and libmp3splt) (Linux, Macintosh, Windows)
MusE, MIDI sequencer (Linux)
Qtractor, A non-destructive multi-track audio and MIDI Workstation (DAW) (Linux)
Rosegarden, MIDI sequencer and multi-track recorder (Linux)
Snd (software), audio editor (Linux, Macintosh)
SoX, command-line multi-track audio editor/processor (Linux, Macintosh, Windows, others)
Sweep, audio editor (Linux)
Traverso DAW (website), a multi-track audio recorder/editor/mixer (Linux, Mac OS X, Windows)
WavePad (website), has a free version sound editor (Windows, Mac OS X)

Converters
Applications Operating systems Misc
MediaCoder Windows, Mac OS X, Linux Audio & video. Batch mode. Use Windows codecs. Open source.
MPlayer Windows, Mac OS X, Linux Audio & video.
Switch Windows, Mac OS X
WinLAME Windows Easy interface.

[edit] Trackers
CheeseTracker, an Impulse Tracker clone (Linux, Macintosh)
Jeskola Buzz, a Modular Tracker system (Windows)
ModPlug Tracker. released as free software in 2004 (Windows)
MilkyTracker. free Fast Tracker clone (Windows)
Psycle is a tracker combined with modular capabilities
Schism Tracker, another Impulse Tracker clone (Windows, Linux, Macintosh)
SoundTracker, a Fast Tracker clone (Unix-like systems)

[edit] Programming languages
Computer music programming languages that are implemented in free software include Csound, SuperCollider, ChucK, Nyquist, and Pure Data.

[edit] Modular systems
jMax
SynFactory
aRts
CPS

[edit] Streaming
BroadWave (website), streaming audio server for Windows
Icecast is a broadcast server to serve audio signals to clients over the HTTP protocol. (Linux, Windows)
PeerCast, a peercasting tool (Linux, Macintosh, Windows)
Firefly Media Server streams music to DAAP clients like iTunes and Rhythmbox (Linux, Macintosh, Windows)
VideoLAN, consists of media and server programs for video and audio streaming. (crossplatform)

[edit] Radio broadcasting
SomaPlayer, radio broadcasting scheduler automation
Campcaster (Linux)
Rivendell (Linux) Complete Open Source radio automation

[edit] Softsynths
ZynAddSubFX (Linux, Windows)
MinimogueVA (Windows)

[edit] Audio analysis
See also: Spectrum analyzer
Praat (Linux, Macintosh, Windows)
Sonic Visualiser (Linux, Macintosh, Windows) [1]
WaveSurfer (Linux, Macintosh, Windows)
BRP-PACU Compares the output FFT (measured) to the input FFT (reference) live signals using the Transfer Function H(f). (Linux)

OTHERS:

Ambisuite- programs for manipulating ambisonic (sound) files.
Free V-AMP- Controller for the Behringer V-AMP2 guitar amplifier
HASAS- HydroAcoustic Signal Analysis System
Ogle- DVD player
Playmidi- MIDI player for GUS, FM, and external MIDI devices
Sound Monitor- Shows esound output
Umix- Adjusts soundcard volume and other features
Xhippo- Playlist manager
aRts- Framework for developing modular multimedia applications
amaroK- Multimedia player for KDE
eSpeak- Multi-lingual software speech synthesizer
jMax- Programming environment for real-time audio
libmodplug- Plays module files (.mod, .s3m, .it, .xm, and more).
octal- Free digital sound workstation for Unix-like systems
speex- Speech compression format
uShare- Is a UPnP A/V Media Server.