Cat I GLS Autoland
Some recent Boeing and Airbus models are equipped with GLS systems qualified for Category I and autoland, as a first step toward Cat III and, for that matter, as an additional opportunity to regularly exercise the autoland functions.
Cat I GLS can be flown at EWR and IAH and perhaps some others by now, but not sure if autoland is available in every case. The key prerequisite is installation of a qualified ground station (GBAS) - GAST C for Cat I and GAST D for Cat III (not yet in service). A key difference is increased signal integrity.
Cat III operations, of course, require more than airborne and navaid systems, they also require an runway/airport infrastructure, especially lights and the low visibility surface movement plan with associated markings, lights, procedures, etc. Nevertheless, as previously mentioned in this thread, the GBAS GAST D would be less expensive than the Cat III ILS installation, plus usable for all qualified runways in the vicinity not just one as with ILS.