Roost is a real-estate search engine with comprehensive for-sale listings in the markets it covers, including for-sale-by-owner listings (which it does not show side-by-side with MLS listings because of industry restrictions). You can see all the photos for a particular house without leaving the search engine, you can see results on a map, and there are sliders (for price, bedrooms, square feet, etc.) to tweak results. It is a pretty-straight-forward site without a lot of bells and whistles.

On the back-end, Roost hosts a directory of real-estate broker sites and delivers search traffic to those sites based on a combination of natural results and paid search.

Above: Roost Screenshot -- #1