Medly - Tap & draw to create your song. No musical skills needed.
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Reason Compact - Reason Compact is a smart, creative application that allows users to compose music by inserting great effects or melodies with an easy-to-use command with powerful beating tools.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::
GarageBand - GarageBand is a fully equipped music creation studio for Mac