via http://www.aep-emu.de/

Marat Fayzullin has ported his (commercial) MasterSystem, GameGear, SG-1000, SC-3000 and SF-7000 emulator MasterGear to the Android platform: MasterGear for Android

Quote:
New in 2.6.13:
  • Added toolbar with links to my other apps.
  • Added multiple Freeze/Restore slots.
  • Worked around an Android bug that prevented some ZIP files from opening.
  • Added third virtual fire button and assigned it to fast-forwarding.
  • Arranged fire buttons vertically in landscape mode.
  • Moved joypad away from the bottom-left corner button in the portrait mode.
  • Added warning bubble when going to the Android Market.