AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
Cubasis - Cubasis is Steinberg’s streamlined, multitouch sequencer for the iPad.
Sampulator - Make (and record) beats on your keyboard
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.
Logic Pro X - Music production.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).