Sega Master System

[Fanatic 64]

"Gearsystem" makes it sound like it's a Sega Game Gear (Sega's handheld console) emulator.

 

[NES_player4LIFE]

His GitHub page says.

Gearsystem
Copyright © 2013 by Ignacio Sanchez

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Gearsystem is a Sega Master System / Game Gear emulator written in C++ that runs on iOS, Raspberry Pi, Mac, Windows and Linux.
The main focus of this emulator is readability of source code with very high compatibility.

 

[Helius]

That's it. It can emulate both consoles.
They have quite similar hardware.