Meludia - Listening exercises and to sharpen your ear and music theory skills
Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
GNU Solfege - GNU Solfege is free music education software.
GNUitar - GNUitar is guitar effects software that allows you to use your PC as guitar processor.
Perfect Ear - A simple yet advanced application for improving your solfege skills.
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.