Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
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.
keezy - A colorful soundboard. Play with music.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
Splice - Music creation, collaboration, and sharing made simple.