Blekko, a new search engine that attempts to use human input to refine search results, launched a public beta on Monday.

Blekko, a new search engine that attempts to use human input to refine search results, launched a public beta on Monday.

The Blekko.com site uses what the site calls "slashtags": a curated list of sites around a given topic. Users can create the sites, and also use them as a search modifier to only search within them.

Blekko will take on Google and Microsoft's Bing, joining a small list of search startups, such as Cuil, that , , and then . But if it goes down, it won't be for lack of a public effort, chief executive Rich Skrenta said.

"Bing and Google have hundreds of contractors that use web tools to refine this relevance data - classifying porn, spam, domain parks, ecommerce sites, fake 404's, markov-spam, official sites, and so on," Skrenta wrote in a blog post.

"As a 20-person startup, we asked ourselves how blekko could assemble this essential data," Skrenta added. "Hire contractors? Use Mechanical Turk? Elance? But - of course! - we know a much better way.... A way you can get orders of magnitude greater participation, while at the same time being very open about the process. Let the public in."

Slashtags filter out so-called "spammy" sites, Blekko said, but depend on the individual creators to edit them and add new sites that crop up. Users can "follow" other slashtags and use them as filters, and also apply to edit them. The site also has a "global chatter" page which auto-tracks updates to the sites and to slashtags, and can serve as a sort of communication medium of sorts.

The search engine also includes an SEO page for individual search results, the ability to comment on a particular site, and even the search result site's IP address, just by hovering the mouse over the link.

Blekko itself curates many of the topics. For example, searching for "technology /tech-reviews" brings up a list of relevant results.

Blekko's initial goal, the company said will be to identify the 50 best sites on the Web for the top 100,000 search categories. Over time, the site will "auto-slash" queries.

At this point, there do not seem to be any "featured" or paid search results, or advertising.

Blekko said it has raised $24 million since its founding in 2007 from U.S. Venture Partners and CMEA Capital, as well as leading angel investors including Ron Conway, Mike Maples, Jeff Clavier, and Marc Andreessen.