orDrumbox - Real-time drum machine and audio sequencer written in Java. Online demo, full download, and user manual. - http://www.ordrumbox.com/
Zinf - An open source audio player for Linux and Win32, supports MP3, Ogg/Vorbis, WAV and Audio CD playback, SHOUTcast/Icecast HTTP streaming, RTP streaming, with a powerful music browser, theme support and a download manager. - http://www.zinf.org/
Audacity - A free, open source software for recording and editing sounds in Linux, Mac OS X, and other operating systems. - http://audacity.sourceforge.net/
SND - Snd is a sound editor that can accommodate any number of sounds and can be customized and extended using either Guile, Ruby, or Forth. - http://ccrma.stanford.edu/software/snd/snd/snd.html
Ubuntu-Studio Project - A site for musicians wishing to use Ubuntu-Linux as their Digital Audio Workstation. - http://ubuntustudio.com/
MP3 Book Helper - Provides Mp3 and Ogg Vorbis tags editing and file renaming functions. (Delphi) [Windows] - http://mp3bookhelper.sourceforge.net/
Open Sound World - Open-source programming environment that allows musicians sound processing in response to real-time control. - http://osw.sourceforge.net
MPEG4IP: open source MPEG4 package - MPEG-4 AAC audio encoder, MP3 encoder, MPEG-4 video encoders, MP4 file creator and hinter, IETF standards-based streaming server, MPEG-4 player. Mostly Linux-based. - http://mpeg4ip.sourceforge.net/