Genesis Plus GX is an open-source Genesis, Master System, Game Gear, SG-1000 and Sega CD/Mega CD emulator by ekeeke. It is based on an older emulator, Genesis Plus, by Charles MacDonald. This older version only supports Genesis.
Download
SVN Build (Wii and libretro only)
Versions
Genesis Plus, while older, is available as a standalone program for Windows and DOS. Genesis Plus GX, however, is only available on platforms other than Wii/Gamecube as a result of being a libretro core for RetroArch.
Compatibility
It is claimed that Genesis Plus GX can reach 100% compatibility with all commercial games released on the platforms it supports, all while being made primarily to run on Wii/Gamecube. It is recommended to use this version instead of the original Genesis Plus where possible.