Bosca Ceoil - A free, easy to use tool for creating music.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
Zynewave Podium - Podium is a modern digital audio workstation (DAW) for Windows.
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.
Renoise - Renoise is a digital audio workstation.
MOTU Digital Performer - Get inspired, then refine your mix — all in a singular workflow.