A free multi-track audio editor and recorder
Audacity is a free, easy-to-use, multi-track audio editor and recorder for Windows, Mac OS X, GNU/Linux and other operating systems. The interface is translated into many languages. The version currently hosted here is 2.1.0 (March 2015). More recent versions than this are available from http://www.audacityteam.org/download/ . Audacity is free software, developed by a group of volunteers and distributed under the GNU General Public License (GPL). Programs like Audacity are also called open source software, because their source code is available for anyone to study or use. There are thousands of other free and open source programs, including the Firefox web browser, the LibreOffice or Apache OpenOffice office suites and entire Linux-based operating systems such as Ubuntu
CECILIA is an environment for music and signal-processing that uses Csound as its underlying audio processing engine. One can think of CECILIA as a completely programmable sound-processing tool, with real-time interactive processing on soundfiles or live
The Mac3Tag tool helps to edit the tag-information of the MP3 files. This small programm is a powerfull alternative for MP3Tag software and is running under almost every operation system like Windows, Mac or Linux.
A sound editor/sequencer which uses the Java Sound API in order to compose digital music
A music score editor
Open Musicwriter is a multi-platform open-source music score editor. It handles MIDI files and MusicXML files.
Play SoundTracker media on your computer.
PlayerPro is a music composer and sound editor ( SoundTracker ) for MOD S3M XM IT UMX . Uses XI, Quicktime or SoundFonts. Currently runs on MacOS and OSX; playback engines also available for Windows and BeOS. Upcoming version 6 will support ALSA (Linux).
QTMAGEAR is an LGPL library for producing QuickTime MIDI movies and SMF(Standard Midi Files). The goal is to produce various alternate implementations (C/C++/PHP/Realbasic) so that developers can incorporate it into diverse development architectures.