BFD:
http://www.fxpansion.com/index.php?page=1 according to fxpansion, BFD is big, and it's drums, and they haven't decided what the "F" stands for. It is a huge, resource-consuming multilayered sample library.
The idea with BFD is something like this: When you trigger a snare hit, BFD plays back the sample from the snare mic(s) PLUS samples of snare recorded through the OH mics, PLUS samples of snare bleed through all the other kit-piece mics, PLUS samples of snare recorded through the room mics, etc and ouputs all these virtual mics to different tracks that you can send to your host (eg Sonar) or mix internally through BFD. So you end up with the actual tracks as though you had recorded a real drum kit in the room, and you can control the amount of room sound, and the distance of the mics from the kit-pieces, and so on and so on. Anytime you trigger a drum in BFD, it's actually playing back like 20 different velocity-layered samples. For every drum.
BFD takes up a lot more system resources than a typical drum machine, but it provides a very realistic simulation of working with real tracks of a real drum kit recorded in a real room. And it's definitely big-- it comes on two DVDs and takes up like 10 gigs of HD space (you'll want a fast, dedicated hard drive).
Cheers.