CP1919 – a synthesis – sequencing tool via the spectral domain – sounds strange, but watch yourself:
also TouchOSC adds Monome (Launchpad) kind of functionality. which is free!Control (OSC + MIDI) Adds Monome Emulation and More
or LoopJ which reminds of iDrum..
and 2 more sequencing tool that can be checked here.Oraison for iPad