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:
The MasterGear 2.6.15, that emulates MasterSystem, GameGear, and their
older siblings, has been released to the Android Market. Changes in
this version:
* Enabled browsing from the file system root.
* Added Russian and Japanese translations.
* Improved virtual joystick look.
* Added frame skip configuration to Settings.