Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.
Poison-202 - Vintage MIDI synthesizer for Mac and iOS
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.
Moog Model 15 - Meticulously recreated rendition of the classic Moog Model 15 modular synthesizer.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
KORG iMS-20 - KORG iMS-20: Transform your iPad into a complete analog synth studio!