I swear I'm not paid by TechCrunch for this stuff: http://techcrunch.com/2012/05/11/from-disrupt-ny-to-a-43-mil...

GroupMe started at the Disrupt Hackathon. But also startups don't just happen over night and the code will probably change drastically once you scale haha. Scalability isn't the primary focus at most hackathons :)