http://www.monocasual.com/giada/

Quote from the site:
"Giada is a free, minimal, hardcore audio tool for djs and live performers. Load or record up to 32 samples, choose to play them in single mode (drum machine) or loop mode (sequencer) and start the show with your computer keyboard as a controller.
Giada aims to be a compact and portable virtual device for Linux, Mac OS X and Windows for production use and live sets."
Might be useful to some as it is now, and worth keeping an eye on. Couldn't get it working with ASIO though - but did manage to have a bit of fun with it through DirectSound. There's also a roadmap and it looks like it's going to a good direction.
edit: added MIDI to the topic title as well