Gearsystem

About

Gearsystem is a cross-platform emulator for the Sega Master System, Game Gear, SG-1000, Sega Mark III, and Othello Multivision, written in C++. It runs on Windows, macOS, Linux, BSD, and RetroArch, and is described as very accurate in its Z80, VDP, PSG, and FM emulation. Supported features include a wide range of cartridge formats, automatic region detection, YM2413 (OPLL) FM sound support, save states with preview and rewind, run-ahead to reduce input latency, ZIP ROM loading, Game Genie and Pro Action Replay cheat support, and a VGM recorder. Link cable support is available for two local desktop instances, covering Gear-to-Gear and Mark III Joy-Joy connections.

For debugging and development, Gearsystem includes a full debugger with a just-in-time disassembler, CPU and memory access breakpoints, code navigation, debug symbols, a memory editor, a trace logger, an IO inspector, and a VRAM viewer for tiles, sprites, backgrounds, and palettes. It also ships an embedded MCP server for AI-assisted debugging with tools such as Claude Code and Codex, exposing execution control, memory inspection, hardware status, and rewind.

Gearsystem is open source and offers downloads for macOS (via Homebrew or as Apple Silicon and Intel builds), along with Windows, Linux, and RetroArch builds. Additional options include portable mode, drag-and-drop ROM loading, command-line ROM loading, and support for modern game controllers.