Genesis Plus GX has been ported to the GCW Zero by David Knight. Genesis Plus GX is a Megadrive/Mega CD/Master System/Game Gear/SG1000 emulator. The source code is forked from the original by Charles MacDonald and heavily modified by ekeeke. The GCW0 port is a joint effort by Shin-Nil and David Knight with graphics assets contributed by hi-ban and Gab1975.

The GCW0 port has had quite a number of changes made including a brand new menu with many configurable features, a plethora of graphical options, autofire, A-stick support, triple buffering, lightgun support (technically 2 player lightgun supported but good luck with that ;) ), FM music support (for SMS compatible games) and more.

Changes:

Update to most recent source code (2016/01/01):
[Core/MD] fixed large ROM (> 8MB) loading accidentally enabling CD hardware emulation
[Core/MD] improved I2C EEPROM boards emulation
[Core/IO] improved control pad emulation (verified on real hardware)
Added build date to menu
Reduced .SRM filesize (requested by kaio)
.SRM files are no longer saved automatically
Toggled performance optimisations no longer affect speed of SVP chip
Numerous small performance optimisations
Added Autofire
Added sound mute option
Added sound lag option
Updated manual

http://boards.dingoonity.org/gcw-releases/genesis-plus-gx/