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.

SparkFun Pro Micro - 3.3V/8MHz : Electronics

Arduino Micro with Headers - 5V 16MHz - (ATmega32u4 - assembled) : ID 1086 : $24.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Arduino Micro — Arduino Official Store

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

Arduino Micro — Arduino Official Store

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

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

Circuit works on breadboard, kills every Arduino Pro Mini when wired together. - General Electronics - Arduino Forum

Squee! It's the cutest, tiniest little Arduino yet! The Arduino Micro packs all of the power of the Arduino Leonardo in a 1.9 x 0.7 (48mm x 18mm)

Arduino Micro with Headers - 5V 16MHz - (ATmega32u4 - assembled)

Arduino Micro — Arduino Official Store

Electronics prototyping board (breadboard) with an Arduino Pro Mini clone and an assortment of switches and wires Stock Photo - Alamy

Sintron UNO R3 Proto Shield Prototype Expansion Board with SYB-170 Min – Sintron Technology

KOOKYE 3pcs Pro Micro ATmega32U4 5V/16MHz Module Board with 2 Row Pin Header for Arduino Leonardo Replace ATmega328 Arduino Pro Mini

Arduino Micro — Arduino Official Store

KOOKYE 3PCS Pro Micro ATmega32U4 5V/16MHz Module Board 2 Row Pin Header for Arduino Mini Leonardo : Electronics