I help run http://nodeknockout.com/, a 48-hour hackathon. It's free and we run it as a service for the community. One or two of the best apps of the contest usually become legitimate businesses.

Not all of that happens in 48hours, there's a lot of strategizing that happens before the competition, and a ton of work that happens afterward. BUT, you can create a hell of an MVP in 48 hours if you know what you need to do.