Arduino Pro Micro - Small Low Cost Versatile Board

Pololu - Arduino Micro

Pro Micro With The Bootloader Black/blue Atmega32u4 5v/16mhz Module Controller Mega32u4 Leonardo For Arduino - Integrated Circuits - AliExpress

Arduino Mega 2560 R3 (Clone) - ElectroPeak

PD Micro

Arduino Pro Mini 328 - 5V/16MHz - RobotShop

SparkFun 12640 Pro Micro - 5V/16MHz

American Raspberry Pi Shop. One stop shop for all your Pi needs. Raspberry Pi add-ons, HATs, accessories, Starter Kit, Media Center kit, RetroPi

Pro Micro Compatible Board - 5V/16MHz

ArduSHIELD most universal shield for ARDUINO ever, 200% funded on Indiegogo - Open Electronics - Open Electronics

Complete guide to Arduino Pro Mini – Robocraze