Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
Virtual MIDI Piano Keyboard - Virtual MIDI Piano Keyboard is a MIDI events generator and receiver.
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.
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.
TH-U - World class guitar amps and effects for PC and Mac
Synthesia - A fun way to learn how to play the piano.