A still very high quality emulator with very high compatibility. Unfortunately closed source (for now) and no longer updated. For this reason, other Genesis emulators have finally caught up and other emulators are on now par with it and beyond in terms of compatibility. The Genesis Plus GX core, available through an emulator known as RetroArch claims 100% commercial game compatibility (which is likely true).
Support for up to 4 (5??) simultaneous people
Can emulate every console, handheld and peripheral released before the Saturn
In-game chat, so you don't have to switch between windows
Every player can share Controller 1 at the same time so you can take turns with single player games
Netplay can be finely tuned to give the smoothest experience possible (with slight input lag)
The emulator is extremely sensistive and desynchs if you focus on another window, move the window around or minimize it
Chat messages appear too briefly on screen
Community content is available under CC-BY-SA unless otherwise noted.