Damian Peckett did something which I would initially think it’s impossible to implement. He made Apple ][ emulator with Arduino-UNO.
How is this possible? Apple ][ had 48 K of RAM but Arduino has only 2K of SRAM? Well he emulates just the video RAM and for BASIC there is just 1K memory, so not the complete memory map is available, but still good proof of concept.
He is generating VGA video signal and use PS2 keyboard. As you can see on this video the emulator is working:
Now if I had some more time to port the code to processor with 48K or more RAM … would have complete Apple ][ on chip and play Karateka :)