Blekko

The company's public launch occurred on November 1, 2010, after three years in development, backed by investors such as Marc Andreessen and U.S. Venture Partners. Blekko's core product was a search engine that utilized a distinctive feature called "slashtags." These slashtags, denoted by a forward slash (/), allowed users to filter and categorize searches, effectively creating curated, vertical search engines on any topic. For example, a user could add '/health' to a query to search only within a pre-vetted list of trusted health websites. This approach combined algorithmic search with a layer of human curation, as the company and its user community actively identified and tagged reputable sites while excluding spam. The platform indexed a set of 3 billion trusted webpages, deliberately excluding what it identified as content farms to improve result relevance.

Blekko's business model was intended to be based on advertising, leveraging the specific targeting capabilities offered by its slashtag system. Beyond its primary search function for general web users, the engine also provided SEO-related statistics and tools, some of which became paid features later on. The company actively campaigned against search spam, even launching a "spam clock" to highlight the volume of low-quality pages being created. In March 2015, the Blekko technology and team were acquired by IBM. The acquisition was aimed at integrating Blekko's advanced web-crawling, categorization, and intelligent filtering technologies into IBM's Watson cognitive computing platform to enhance its data analysis capabilities. Following the acquisition, the Blekko search engine service was discontinued.