Firmware
It is important to remember that the Duplicator 6 is pretty much a clone of the Ultimaker 2. As such, all firmware for the D6, like the Ultimaker 2 is based on the Marlin firmware. Marlin is an open source firmware for the RepRap and Ultimaker family of 3D printers. It became a standalone open source project on August 12, 2011 with its Github release. Marlin is licensed under the GPLv3 and is free for all applications. Since Marlin is GPLv3, whomever publicly posts a compiled *.hex file, SHOULD also post the uncompiled source code for their branch.