These are the only ones we know about (and I think 1/2 of those are dead): http://code.reddit.com/wiki/PoweredByReddit

The goal with open sourcing was never to have clones -- it was to get people to dev the features that they felt were important but we did not, or did not have the time for. Being able to make an easy clone was just a side effect.

I really like http://lesswrong.com -- a spinoff of http://overcomingbias.com

Their 'stacked' view of threaded comments makes a lot of sense to me. It might be really nice for a code editor too -- the minimal indent width can be smaller, and context is clearer.

Lesswrong is awesome. It is my favorite reddit derivative.