Yes, there's a few.
Blades against Darkness and Scum & Villiany are the two probably "closest" - I think they were both of the KS perk hacks. A number of people are doing third-party hacks. There's an active G+ Community that has a lot of chatter about these things.
A decent Google Doc (that you can suggest missing things) has been started from the G+ community - check it out here.
It's been mentioned that John doesn't want any "full blown" hacks out there till the full release of the game - which will have a bunch of information on ways to change/hack BitD. Many people are already experimenting though!
Edit:: Oops, forgot to link the G+ community I mentioned.