A toy implementation of a monochrome raycast 3D-renderer, on the Arduino-based Arduboy.
This device features a 128x64px black-and-white display, 2.5KB of RAM and 32KB of static Flash storage (most of which I use to store the look-up tables). The CPU is a fairly beefy ATmega32u4 running at up to 16mhz, but doesn't provide an FPU nor even a barrel shifter. Ergo: division and multiplication, even by powers-of-2, is glacial.
If you want to build- and run this on Windows I have an SDL-based version here, for Visual Studio. I use the PC-build to generate the lookup-tables.