CADTrac

The closest to LifeTrac in terms of flexibility is CADTrac - which is what Marcin intended to build initially and even bought the plans. However, the CADTrac is about 3x lighter, has 3x less power, and takes about 10x longer to fabricate compared to LifeTrac. It costs about the same to build as the current LifeTrac, so Marcin never ended up building the CADTrac.

http://www.cadplans.com/cadtrac.htm