With the multitude of distributed version control systems now available, it's getting pretty hard for any open source project to get by on a centralized system. Distributed systems like bzr, mercurial, or git give equal tools to all contributors, not just a select few trusted to vette changes for inclusion in an official branch. Forcing new contributors to work with diff and patch is just plain mean!
So, while Twisted's source is still hosted in subversion, and likely will be for some time to come (due to various toolchain requirements), I'm happy to announce that there is now a git mirror to complement the existing bzr mirror.
With these mirrors available, developers who don't have commit access to the subversion server can still work with Twisted using modern revision control tools - branching, merging, history, and all the rest.
The workflow for merging changes based on the bzr or git mirror back into Twisted trunk isn't yet completely worked out. Likely it won't be until people start using these and trying to push changes back to us. So if you're a fan of one of these two systems, please, start using these mirrors and help us figure out the best way to integrate things back into subversion.