It's a new sega emulator from Steve Snake (the Kgen guy, remember him?). He's got sms, game gear, the sg-1xxx systems, genesis, 32x, sega cd, and 32x cd (that actually works!) in one emulator, an evolution of kega! It even lets you use the mouse to play Mega Mouse or Menacer games!
I found it at Eidolonn's Inn.
It's really cool, and in terms of compatability it seems superior to gens (with the exception of one or two games I tried, like the Bomberman 8 player demo).
Of course it's lacking one major thing, online play! If anyone has contact with Snake, please let him know that kaillera support would be great.
Not to knock gens or anything, I love that emulator, but I think now it really has some serious competition!