GUS Simpson is a experimental grounded delta robot 3D printer prototype, built in 2013 by Nicholas Seward in Hot Springs, Arkansas, USA. Simpson is named after George Gaylord Simpson who came up with the idea of Quantum Evolution, the theory that evolution can happen in abrupt burst. The name signifies that this is a quick divergence (idea to first print in 1 month) from other existing designs.
While reportedly in the works, there is currently no firmware which allows the GUS Simpson to appear like a standard cartesian 3D printer. Thus, you cannot just send it gcode directly from your slicer and expect anything other than utter havoc.
Printing is currently achieved using any vanilla firmware which can directly control X, Y, and Z steppers, using a gcode preprocessor to transform the cartesian gcode commands into something that makes sense for the delta configuration of the GUS Simpson. With this method, it makes no difference which firmware you use (Repetier is used by the original author). If you do this, make sure you don't forget to always use the gcode preprocessor or bad things will happen!
At this point the GUS Simpson cannot produce the dimensionally accurate parts required for self replication.