SourceForge was a huge blunder. They were so close to being Github, but they opted to to squeeze out every last dollar, instead. ExpertsExchanges and AIM are similar--products that could have been medium-large opportunities today, but business and product choices that left an opening for a competitor.

That said, I'm not convinced SourceForce could have actually been Github because it didn't have the culture, the brand was mispositioned, and it's hard to to be Github without lots of VC.