LMMS - Make music with a free, cross-platform tool
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
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.
FamiStudio - FamiStudio is very simple music editor for the Nintendo Entertainment System or Famicom. It is designed to be easier to use than FamiTracker, but its feature set is also much more limited.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
MOTU Digital Performer - Get inspired, then refine your mix — all in a singular workflow.