You can also use a P2P Kaillera client with GENS for netplay.
Review
PROS
Support for up to 4 (5??) simultaneous people
No fiddling with router settings and port forwarding
Netplay traffic is handled by a central dedicated server that helps keep things synched
Private game chat support and public chat to speak people outside your game room
Being able to drop out of a game at any time without disrupting (much) your teammate(s).
Kicking/banning/muting people from your room
It's a matchmaking service where you can join other people's rooms, too
CONS
Supports only Genesis/Megadrive, Sega CD and 32x games
Dropping out of a game is a bit different than with standard emulators
Everyone needs to have the exact same ROM version or Netplay won't work (if it somehow does, it'll desynch rather quickly)
Everyone needs to have the exact same save file, or no save file at all. Else, it desynchs
You need to constantly switch focus back and forth between chat and emulator window in order to chat.
You will hear no sound while the window is unfocused.
It's slightly (significantly still) prone to freezing/crashing/BSOD (in that order)
Random, inconsistent FPS drops due to the server trying to keep everyone synched, sometimes stuttering. It's annoying, but rarely does it make it unplayable
