The NanoPI NEO is a little 8 dollar ARM device with an interesting form factor and specifications.

• 512/256 MB ram (single slot)
• Cortex-A7 Quad-Core
• USB 2.0
• 100 Mbps ethernet
• 40 x 40 mm board size
• SD card slot

Mainline support

FriendlyARM provides an UbuntuCore image, but of course …