pattern sequencers

I've been playing with the Korg I.K. oscilator a lot, and though it's awesome it made me start to wonder. Do any of you know of a pattern sequencer app, like Band in the box for windows? That is, you have various preset patterns or loops, as well as the ability to build your own loops from the ground up, but then you can change the chords the loops are playing in. I can do it with Korg, but to change chords I have to change almost every part of the loop, so this kind of app would be very useful. Any ideas?