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 pinout diagrams are simple, but they're easy to read, and especially helpful for beginners. You can print them out full size so you can set your Arduino Uno, ATMega, or ATTiny right on top for ...

Scheduled to appear in late May, Uno R4 will come in two versions: the plain ‘Uno R4 Minima’, and ‘Uno R4 WiFi’ with an Espressif S3 WiFi module that also gives it Bluetooth Low Energy. “We ...