LMMS - Make music with a free, cross-platform tool
keezy - A colorful soundboard. Play with music.
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Aftertouch - Aftertouch – 3D MIDI Controller created and published by Kevin Nelson.