For being free, this is actually a great little bit of software that I got pointed towards from a friend. It's simple, but has a decent sound, and with a little distortion (I personally like Sausage Fattener), it sounds frickin' PHAT. I highly recommend it if you don't have access to really high end soft synths.
I use this free little bass plugin very often. It's simple and sounds amazing. Would recommend to anybody! EDIT: I've been missing this plugin since I switched to Mac!