LMMS - Make music with a free, cross-platform tool
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
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.
ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
zMors Modular - Full featured modular synthesizer for iOS