Jaanus has been working on a subminiature Arduino clone which be believes is THE smallest.
Everybody are making Arduino clones. So I thought I should make THE smallest. I took smallest package atmega88 – qnf28 (5mm x 5mm). Routed smallest possible resonator and as much pads as i could fit on in.
His design provides SPI, UART, one LED and breaks out 4 analog and 1 digital IO pins.
Check out Projects of Jaanus for project details, design files and related docs.