MLRV is a free sampling instrument designed for live performance with grid controllers like Akai's Mp x series and the Monome. It runs with Max/Msp (and can therefore be heavily customised), although Pc and Mac users alike can download a free runtime if they don't have that software.
I'm not entirely sure how its functionality differs from Ableton Live's, so I'll have to wait until the first of February, when it becomes available for download. Here's a beautiful live demonstration by Galapagoose:
Check out the MLRV 2 in greater detail.