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
EasyABC is an open source ABC editor
EasyABC allows the user to create, edit, view, play, convert music written in the ABC music notation language. The program was written in Python 2.7 and WxPython by Nils Liberg and runs on Windows, OSX, and Linux. Nils Liberg is no longer supporting this open source package, however I have volunteered to continue its support and development.
A general tool for creating and processing sound in a general manner. The plug-in system makes it possible to create a complete software studio with all kinds of cool little boxes.
EasyTAG is an utility for viewing and editing tags for MP3, MP2, MP4/AAC, FLAC, Ogg Vorbis, MusePack, Monkey's Audio and WavPack files. Its simple and nice GTK+ interface makes tagging easier.