Founded: 2004 (acquired by Google in 2005)
What it could have been: The service that put check ins on the map.
Still extant? No–Google closed it in 2009.
What went wrong? Dodgeball was a mobile service for checking into real-world locations, an idea that eventually became extremely popular. But maybe Google was just too early: In 2004, very few people were familiar with the idea of phone-based social services. (Engadget called Dodgeball “Friendster for your cellphone.”)
Random trivia: Dennis Crowley, founder of Dodgeball, went on to create FourSquare–basically the same thing with much better timing.