The loved/hated Yoshihiro formerly from WAB team has released a Sega Master System emulator which is a port of the MasterGear non Open-Source emulator.

Here’s what they say on their homepage:

Boutton :
TRIANGLE  : used in game to return to the browser and load another game :)
CIRCLE    : it’s the boutton 2 of SMS paddle & GG
CROSS     : it’s the boutton 1 of SMS paddle & GG
START     : Pause
SELECT    : Sound on or Sound Off

New :
GPU Full screen added for the sms roms
Stretch screen for the GG roms
and some Fixs .

..:::: soon ::::..
Speed fix at 60FPS with the GPU .
sound fix at 44100 . 80% done
add The sega sg1000 support . 50% done
add the coleco support (it’s a clone of the sg1000); 50% done