The UltiMainboard 2.x.x electronics are released under GPLv2 license.
And are based on the origonal Ultimaker electronics design by Jan-Jaap Schuurman, Siert Wijnia and ErikDeBruijn at http://reprap.org/wiki/Ultimaker's_v1.5.7_PCB
As well as the ArduinoMega2560 by Arduino: http://arduino.cc/en/Main/arduinoBoardMega2560
