Smallest unit in KiCAD is 1 nm. This is (1/1 000 000)-th of millimeter.
Quite precise for PCB design!
For comparison the popular Eagle CAD base unit is 1 um which is 1000 times bigger, so KiCAD uses 1000 times more precise metrics than Eagle.
Actually lot of the modern chips today are made on 28-40 nm technology.
So maybe KiCAD designers when deciding to use 1 nm as smallest unit were thinking too expand KiCAD as ASIC mask generation tool in future?
…who knows 🙂
Random.org say our winner is @trebadur please send us your address to info@olimex.com to send your prize
olimex 
Jul 10, 2016 @ 10:12:59
Nice PCB design, but there is a mistake, a trace is connecting with a via but without connection at the other end, is KiCad able to detect this faulty ?