SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::
FamiStudio - FamiStudio is very simple music editor for the Nintendo Entertainment System or Famicom. It is designed to be easier to use than FamiTracker, but its feature set is also much more limited.
cassini - Polyphonic Synthesizer for iPhone/iPod touch