This is quite possibly the best Genesis emulator for development and hacking. It has everything you could possibly want except for the two most important things (in my opinion): a tracer and an interactive debugger. The author has said that the way Gens (the emulator this is based on) works, it will require a lot of breaking and gluing back together, in a manner of speaking, to properly implement.

Gens KMod website: http://gendev.spritesmind.net/page-gensK.html