Giada - Giada is a free, minimal, hardcore audio tool for DJs, live performers and electronic musicians.
Studio Amplify - Create cutting edge music and audio apps
JAM - Shake your sound - Music motion app. Make music by shaking your phone. 🎶
Groovebox: Beat & Synth Studio - Make Music & Play Instruments
Blocs Wave - A free audio app for creating music loops.
Theremin - Multitouch synth instrument that makes an array of sounds