Violin by Trala - Violin by Trala is a music learning app that is designed specifically for Violin users.
Guitarix - Guitarix is a simple Linux Rock Guitar Amplifier for https://alternativeto.
Metronaut - An app to help you play classical music
GNUitar - GNUitar is guitar effects software that allows you to use your PC as guitar processor.
Flat - Online collaborative music score and tab editor, accessible from any device
Ampire - State Space Modeled guitar amp/cab/stompbox simulator.