LMMS - Make music with a free, cross-platform tool
GoatTracker - This is a crossplatform C64 music editor.
Ardour - Record, edit, and mix on Linux, Mac OS X, and Windows.
1BITDRAGON - 1BITDRAGON is a user-friendly music creation software that allows anyone to make music without having to be an expert or have thousands of dollars of gear.
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
Jummbox - A modified Beepbox that have more stuff then Beepbox. It can be used just like Beepbox. The features of Jummbox is the same of Beepbox's features, but Jummbox have more stuff to offer.