EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
GNU Solfege - GNU Solfege is free music education software.
TH-U - World class guitar amps and effects for PC and Mac
LenMus - LenMus is a free program for learning music.
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.