TouchDAW - Full-featured DAW control and general purpose MIDI control app.
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
XotoPad - MIDI instrument controller with chords, scales, faders, and more for multi-touch Windows devices.
Guitar Pro 7 - Create, play and share your tabs
Midi Studio - Full-featured, modular MIDI control surface for iOS
Synfire - The comprehensive Music Prototyping Studio for professionals and enthusiasts.