A new realtime search engine called Wowd is launching publicly today at the Web 2.0 Summit in San Francisco. Founder and CTO Boris Agapiev gave the first public demonstration of Wowd at our Realtime Stream Crunchup last July (see video below). Wowd takes a very ambitious approach to search in that it is a peer-to-peer search engine. Users download a peer-to-per client and the index exists not on any central cluster of servers, but across all the user’s machines. Agapiev, who formerly founded the vertical search engine Vast, set out to conquer scaling issues in a new way and settled on a P2P approach. What makes Wowd a realtime search engine is that ranks sites based on how often and recently the Wowd community has visited that site. On Wowd, you vote with your mouse, so to speak. The search engine uses other more traditional ranking algorithms as well, but its main point of differentiation is the realtime clickstream data it gets from the peer-to-peer clients which it wants users to download. In theory, this will provide Wowd with your complete attention history if you allow it—every site you go to, not just the ones you click to from the search engine (in this regard, it is similar to what the Google toolbar records if you have the Web History feature enabled). As with any attention recorder, Wowd offers a full range of privacy settings so that you can share only what you wish, and it is all anonymized and Wowd doesn’t even know your IP address anyway. You can always see and search your entire Web history, which is helpful when you are trying to remember that obscure furniture site you saw last month. Nevertheless, this will be a big barrier for many consumers who might not feel comfortable sharing their surfing habits with an unknown startup. Simply asking people to download a client will be a barrier to adoption. But for those who do, they will be presented with a slightly different search experience. Results are ranked based on which sites are most popular with the Wowd community. Sites that have been visited recently get a stronger weighting. You can also switch to see the freshest results. The quality of the results depend on the Wowd community’s finding and visiting the best sites, but it is all based on passive activity. Wowd’s results supposedly won’t be as susceptible to SEO spam as other search engines. But if it becomes popular enough I’m sure spammers will try to game it by simply getting lots of people to download Wowd and visit their own sites continuously. Wowd obviously tries to monitor this type of behavior and weeds those clicks out from results. I’ve been testing Wowd for a coupel months, and the results are decent already with only a few thousand beta users. Now that Wowd is open to the public, the real test will begin. Realtime search is hot right now, with tons of startups (Collecta, OneRiot, Topsy) and as well as bigger companies like Twitter, Facebook, and Google going after it.