Syntheogen™ is a step sequencer and synthesizer I developed for Android phones and tablets:
Syntheogen was mostly written with C++ and the Android NDK. Production builds target Android, but the app also runs on Windows, which I use for development and testing.
The interface was built on a custom GUI framework, and specifically designed to support touchscreen devices. The sequencing and synthesis engines are also custom designs, and the sequencer offers features not found in other music apps: measures can be sized and divided almost arbitrarily, patterns of different length can be mixed in the same loop, and notes can be tied to produce legato phrases of any length.