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
Audio Tag Editor
Kid3 audio tag editor can edit the tags of MP3, Ogg, FLAC, MPC & WMA files in an efficient way, convert between ID3v1 and ID3v2, set the tags of multiple files, generate tags from file names or vice versa and import from freedb, MusicBrainz and Disco
Audiobook Cutter is an easy-to-use tool which splits large speech MP3 files into smaller ones without re-encoding. The split points are determined by silent parts. The main purpose is to make audiobooks or podcasts more manageable in a user-friendly way.
Open-source alternative to Propellerhead Reason
The Calopsita project is a free, open-source alternative to Propellerhead Reason. I am currently looking for programmers, designers and testers.
free cross-platform music creation software
LMMS is a free cross-platform software which allows you to produce music with your computer. This covers creating melodies and beats, synthesizing and mixing sounds and arranging samples. You can have fun with your MIDI keyboard and much more – all in a user-friendly and modern interface. Furthermore LMMS comes with many ready-to-use instrument and effect plugins, presets and samples.