There's some forks floating around, but nothing major. I think there's one that fixed the bug with PSN PSX games on 6.60Pro-C2, so that's great if you want both PSN PSX games and the newer noDRM engine. For the most part, I just stick to 6.60Pro-C (fix 3). If you want something else to tinker with, you can check out the ME CFWs. They have different options than Pro. Not really more, just different. There's little reason for new CFW since there's not any new OFW, and there probably never will be again for the PSP. Now people can just hunker down and come out with well optimized homebrew for the PSP without having to worry about it changing.