Hi5, once one of the top three global social networks, was acquired by San Francisco-based Tagged on Wednesday, as some of the remnants of the social network space clear out in the wake of Facebook's overwhelming dominance.

Back in 2008, hi5 trailed in popularity only behind MySpace and Facebook. In June, News Corp., which owns The Wall Street Journal, sold MySpace for just $35 million, a major comedown for a company that was purchased for $580 million.

The...