I was investigating handheld game systems on microcontrollers when I discovered RomanS’ ESPBoy and corax89’s ESP8266 game engine (game library) and the espico game engine.
In addition to these, the ESP8266 is capable of emulating ZX Spectrum and Chip8/Superchip. You can port Arduboy thanks to hartmann1301’s Arduboy2 fork, cheungbx’s esp8266_arduboy2 and edgarborja’s Arduboy2ESP library. Finally, there is MicroPython.
The most interesting to me is corax90’s library. Having a small library of modifiable games is what drew me to Arduboy previously, I don’t necessarily intend to develop my own games but it is very helpful to be able to modify existing ones.
https://www.invidio.us/watch?v=GVg4Ar-J3tM (with ESPert)