I've made a lot of fixes and improvements to LividStep since I first put it out there. It's designed for our Ohm64 and block controllers. Even if you don't have one of our controllers, the m4l device is worth a look, and adaptable to other devices. It centers around live.step, but takes over the clock so it is completely warpable. It uses 8 steps, but allows so much variation, that 8 steps is plenty for building up a track.
An overview video (a bit dated, as it doesn't have the changes):
(yes, I posted this on the ableton m4l forum, too - gotta let y'all know!)