I've designed and built two major iterations and dozens of minor iterations of an advanced FDM 3D printer for my company
Praxis Mfg. The current version has automatically switched tool heads similar to E3D's system, a touch probe measurement tool I built from scratch, a novel 5-axis motion platform uniquely suited to FDM, and a robust softare calibration routine for that platform. The calibration routine allows an inexpensive precise-but-inaccurate system to achieve < 0.05 mm positioning accuracy throughout a 280 mm x 280 mm cylindrical working volume.
This page will be more interesting after I get around to filing IP protections for Praxis.