Arduino Micro Pro R3, BreadFruit Electronics

The Arduino Micro is essentially a shrunk-down (1.9″ × 0.7″) version of the Arduino Leonardo: it is a microcontroller board based on the ATmega32U4 running at 16 MHz with 24 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs). This board ships with the male header pins soldered in.

running at 5V/16MHz Supported under IDE v1.0.1 On-Board micro-USB connector for programming 4 x 10-bit ADC pins 12 x Digital I/Os

OSOYOO Pro Micro 5V/16MHz Module Board with 2 Row pin Header Replace wit Pro Mini for Arduino

Pro Micro & Fio V3 Hookup Guide - SparkFun Learn

Pro Micro & Fio V3 Hookup Guide - SparkFun Learn

Arduino Pro Mini, BreadFruit Electronics

Arduino Pro Mini 328 - 3.3V/8 MHz : ID 2377 : $11.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Pro Micro - 3.3V/8MHz - DEV-12587 - SparkFun Electronics

Arduino Lilypad, BreadFruit Electronics

3-Pack Arduino Pro Micro 3.3V from ElectricDream on Tindie

Arduino Micro — Arduino Online Shop