Developer boards now allow end users to realise complex circuits in the smallest of spaces, but Itaca Innovations is taking space-saving to the next level with the uChip, which is just 28.5 x 10.6 mm. The Arduino Zero compatible board is no bigger than a large coin and is currently being funded on crowdfunding website Kickstarter. ITACA estimates to ship the uChip from June this year for early-bird backers.
https://www.notebookcheck.net/uChip-An-ultra-compact-Arduino-Zero-compatible-board-that-costs-just-EUR20-US-22-45-pound17-15.413852.0.html