iDensity is an interesting take on granular synthesis, in a straight-forward package. All of your controls are presented on one page with a series of sliders to control things like grain size and randomization. I found it to be pretty fun for drones, but without any MIDI or even an on-screen keyboard, drones are pretty much what you'll be limited to. If you want musicality in your granularity you should consider SampleWiz or Curtis; both of which offer on-screen keyboards and AudioCopy/Paste. Watch a full review here.
Disclosure: I received my copy for review from apeSoft.