Contraptor is a DIY open source construction set for experimental personal fabrication, desktop manufacturing, prototyping and bootstrapping. Various сartesian robots can be assembled from Contraptor and used as a prototyping platform for projects such as XY plotter, mini CNC machine, 3D printer etc. Contraptor uses several developments of the Reprap project - specifically, Stepper Motor Driver boards v1.x and Arduino GCode Interpreter.
The main project site is here: http://www.contraptor.org
The Contraptor site gives detailed instructions on how to make each Contraptor part using widely available raw materials and simple hand tools to drill the standardized holes. Or you could buy the parts pre-drilled from various suppliers ... If you bought the pre-drilled $300 "Mini CNC subset kit without electronics & motors" and the $200 "Electronics & motors subset kit with Arduino", is there anything else you need to build a RepStrap?
- (Does this have a catchy name yet, like other RepStraps?)
An effort is underway to build a Repstrap and/or Milling/Repstrap hybrid on the Contraptor platform, most likely using mini CNC contraption as a base: http://www.contraptor.org/mini-cnc
"Mini CNC case study" has photos of a router with a 8"x6"x1"(?) working volume working volume built with a Contraptor frame, Dremel toolhead, and RepRap electronics. That page also links to the open-source (?) plans for that router on Google Sketchup. That page also discusses building much larger CNC machines; other CNC machines built with Contraptor.
- Mini CNC case study 
- Contraptor mini-cnc with Reprap firmware. (has this been reported upstream?)
- Contraptor Mini-CNC Build log.
- Super mini bootstrap CNC  discusses building a one CNC machine mostly out of Contraptor parts that is designed to drill all the holes needed to convert aluminum angle into more Contraptor parts -- does this meet the definition of a RepRap, not merely a RepStrap?