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

Gearsystem is a Sega Master System / Game Gear emulator written in C++ that runs on iOS, Raspberry Pi, Mac, Windows and Linux.

Features

Highly accurate Z80 core.
Multi-Mapper support: SEGA, Codemasters, and ROM only cartridges.
External RAM support with save files.
Automatic region detection: NTSC-JAP, NTSC-USA, PAL-EUR.
SMS2 only 224 mode support.
Internal database for rom detection.
Sound emulation using SDL Audio and Sms_Snd_Emu library.
Integrated disassembler. It can dump the full disassembled memory to a text file or access it in real time.
Compressed rom support (ZIP deflate).
Multi platform. Runs on Windows, Linux, Mac OS X, Raspberry Pi and iOS.