In 2001 I've written my own Sega Master System and Game Gear emulator completely from scratch in ANSI-C for the Sega Dreamcast and the Gamepark GP32.

There's a new version which is rewritten using proper object-oriented C++. Furthermore, it uses cmake as the build system and SDL2
as a cross-platform software development library. There's a new debugger with wla-dx compatible symbol file support. The debugger might be quite basic right now, but it will hopefully be a powerful tool for SMS/GG homebrew software development in the future.