The booking engine (based on reading the url's) is Pegasus, used by Travelweb, and many other hotel booking sites, including Marriott's. Each site supplies its own look & feel, somewhat, just like United and itn.

One interesting result is that they seem to use a common cookie, so that date & hotel program info you enter when booking or shopping on Sheraton's web site, for example, is retained if you then go to Marriott or Travelweb.