zMors Modular - Full featured modular synthesizer for iOS
Serum - VST for FL Studio, Ableton Live, and many other VST supported DAWs. Heavily utilized in EDM.
ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Omnisphere - Piano, pad and synth VST for DAW's.