MilkyTracker - MilkyTracker is an open source, multi-platform music application for creating .MOD and .
Virtual MIDI Piano Keyboard - Virtual MIDI Piano Keyboard is a MIDI events generator and receiver.
OpenMPT - OpenMPT is a popular tracker software for Windows.
EveryonePiano - Everyone Piano is the best free computer keyboard piano software, which supports downloading 3 types of music score formats like stave, right and left hand numbered musical notation and EOP file.
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.
Synthesia - A fun way to learn how to play the piano.