Pro Micro - 5V/16MHz - Arduino-compatible ATmega32U4
Spice up your DIY keyboard builds with this little microcontroller, which works with the TMK and QMK firmware. It's got 18 pins for you to work with.
The ones currently being sold are black PCBs.
Note for Blue Pro Micros purchased after April 8, 2020: In the most recent batch of blue Pro Micros, the USB hardware IDs are different than usual, so if using QMK Toolbox to flash them, make sure you use the latest version of it (0.0.18 or higher): https://github.com/qmk/qmk_toolbox/releases/tag/0.0.18