Many other boards are huge.
Here is a very tiny arduino board.
After you'r polished the project enough, time to pack it.
Only 12.5mm X 25.5mm in size!
Can be flashed with arduino bootloader before or after soldering.
All pins are exposed on the back-board.
22 pads plus serial and additional power via 1.27mm pin header.
Version 0.9 is a complete version for now.
Unlit bug being found.
Free for privet use.