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.
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
Beat snap 2 - Beat snap 2 is a smart sound & music management application that lets you create marvelous symphonies or compositions by setting the beats or genres, such as Trance, House, Techno, Drum, Bass, Pop-Rock, Rap, Hip-Hop, Dubstep, and Trap, etc.
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::
GarageBand - GarageBand is a fully equipped music creation studio for Mac