Hydrogen is an open source drum software program. I just discovered this today and I thought I'd rave about it a little. It runs under Linux and you can get it FREE at http://hydrogen.sourceforge.net/ I've never used a drum machine before, either software or hardware, and I found it very easy to use. It's not real sophisticated, but it sounds good and has some nice features. There are custom drum kits you can load in, and I think it has some sort of MIDI capability. If you're a Linux user, check it out. Otherwise change operating systems.