From one of the original creators of MbUnit comes Pex - automated unit test generation.

"Pex generates Unit Tests from hand-written Parameterized Unit Tests through Automated Exploratory Testing based on Dynamic Symbolic Execution"

I've read bits and pieces about Pex before, but now there's something to download.

Jeff Brown shows how you can use Pex with the latest Alpha release of MbUnit's Gallio test runner.