Tape It - App for songwriting & audio recording.
Giada - Giada is a free, minimal, hardcore audio tool for DJs, live performers and electronic musicians.
Songcraft.io - A platform for songwriters to write, organize & collaborate.
Loopy Pro - Loopy, the sophisticated, tactile live looper app that reinvents iPhone and iPad music making.
RiffShare - Write down a musical riff, send to band members, collaborate
Group the Loop - Live Looping with usefull GUI, Verse/Chorus layer system, drummer, effects, etc...