Jaanus Kalde has made the Tinydino, an Arduino clone that’s just 7.4 mm square. He used the ATmega88 chip and built the rest of the components around it. According to Jaanus, its features are:
-Auto reset -UART -SPI -4 analog channels -1 digital i/o -one LED -funny readme with BOM
It needs arduino bootloader for atmega88 like ottantotto bootloader, probably it needs some hacking too because the resonator is 8MHz not the Arduino regular 16MHz.
[via Electronics Lab]