What it could have been: Twitter, at about the same time Twitter was getting going.
Still extant? Yes. Google gave up on it in 2009 at the same time it axed Dodgeball, but open-sourced it. But it’s in pretty sad, spam-infested shape.
What went wrong? You know, I’m not sure. It was one of umpteen services that Google has bought over the years and then not done much of anything with. Scary thought: If Google had acquired Twitter rather than Jaiku, it seems entirely plausible that Twitter might not exist today.
Random trivia: Like Twitter, Jaiku has a 140-character limit, originating from its beginnings as a text messaging-oriented service.