The Arduino Uno-compatible board has an MCS-51 (often called 8051 instead) instead of the usual ATmega328P/ATmega168. Specifically, [ElectroBoy] uses the AT89S52.

The vertsatile Uno Rev3 is capable of more than just a board for experimental and education projects ...

If you really want to show off your DIY skills, Arduino projects can be useful, beautiful, and impressive. Check out some of our favorites.