Twitter was an offshoot of Odeo, an otherwise unpromising podcasting startup. Yammer, a Twitter clone launched at the TechCrunch50 conference, even copied the origin myth; it sprang from the loins of Geni, the $100 million genealogical website started by former PayPal executive David Sacks. Like Facebook, users sign up with their work email address as a way of verifying that they're employed by a company. Yammer's positioned as a tool for coworkers to keep track of each other's status, with features missing in Twitter such as threaded comments, tags, and messages longer than 140 characters. Even more interesting: In a panel following the demonstration of the site, Salesforce.com CEO Marc Benioff said he's interested in buying the whole thing. At last, something resembling an exit for Geni.

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