ReplicatorG development is discussed on a list hosted at Google Groups:
What's it for?
This list is for people who are actively interested in writing code for either ReplicatorG or a codebase associated with ReplicatorG (like a GCode generation engine or firmware for a CNC device). If you're looking for help using ReplicatorG, we recommend instead checking a support group for your machine, like the Makerbot Operator's Group. If you think you've found a bug or have a feature request for ReplicatorG, please see our page on reporting bugs.
The list is publicly readable, but membership is moderated to reduce spam. If you want to jump in, just click the "apply for group membership" link with a quick note indicating that you are not a robot selling Cialis Toothpaste or whatnot and we'll get you set up as soon as we can.