Noteflight
Noteflight focuses on online score writing and collaboration.
What it does
Noteflight supports online score editing and collaboration.
When to use it
A teacher and student can revise notes in the same practice piece.
Visit Noteflight official site
Amped Studio
Amped Studio focuses on browser-based recording and multitrack production.
Ardour
Ardour focuses on recording, composition, and mixing workflows.
Audacity
Audacity focuses on waveform editing, recording, and audio effects.