i was going to recommend max...until i opened the thread

cant think of anything else off the top of my head.- going to require detailed programming whatever you use

for software try battery or fruity loops fpc for hardware look into the korg er line of synths

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Stylus rmx has a chaos feature that will do what you're after, and will also accept your own drum loops. It's not cheap though....but cheaper than their other vstis.

Maybe not exactly what you're looking for, but it can do some pretty good stuff.

http://bram.smartelectronix.com/plugins.php?id=6

It's a plugin called Supatrigga. When synced to your hosts tempo, it slices and shuffles incoming audio (usually drumloops) in the rhythm. Check the demo's...