Carla is a fully-featured modular audio plugin host, with support for many audio drivers and plugin formats.
Surge
A sound designer’s dream. A friendly, open community.
solfege
When you study music on high school, college, music conservatory, you usually have to do ear training. GNU Solfege tries to help out with this.
Minit
Minuet is an application for music education. It features a set of ear training exercises regarding intervals, chords, scales and more.