Founded in 2005, Powerset's first product is search engine for Wikipedia.
So after google, we now have a dedicated wiki search. But do we need it and isnt google more effective. To a certain extent yes, but if you want a detailed and in depth search on Wiki than Powerset seems to be an awesome solution. You can type sentences, phrases or keywords and Powerset will get you the closest answer in Wiki and sometimes even gets the correct answer directly. Besides Wikipedia, Powerset also get the articles/responses from Freebase which is an open community with tons of information.
Though fundamentally it s a search engine and there's nothing much to differentiate except that its in a niche segment - Wiki Users.
To check if it works well hit http://www.powerset.com/