What are some alternatives?
Sampulator - Make (and record) beats on your keyboard
Audulus - A universe of sound at your fingertips - Audulus is a modular music processing app
NanoStudio - NanoStudio is a recording studio for iOS, OS X and Windows.
Silenz - Mix ambient noise in with the music you're listening to
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
CodingRadio - Code with epic background music tracks 👨💻🎧