Biz Stone cofounded Twitter about 10 years ago. Now, he's building Jelly, some kind of mix between Google and Quora. There's an interesting bit on this Josh Elman article from TechCrunch: 

The future of search lies with human conversations, not a list of links. Traditional web search excels at providing ranked search results, but results can be dated or only tangentially relevant, and search engines can’t answer subjective questions. Humans, in contrast, can provide direct and relevant answers to complicated questions. Biz believes that tapping into a network of people is the best way to find answers utilizing network intelligence to search and find the most pertinent and useful information.

And also a pro tip for entrepreneurs: 

In his pursuit of building Jelly, Biz learned the valuable lesson that every company should be prepared for massive viral growth. When he first launched Jelly, the response was overwhelmingly positive, and they had about a million downloads in a just few days. But his team wasn’t prepared for the influx of users — they had yet to generate enough helpful content and create an engagement loop to keep users coming back, which ultimately stagnated its growth. ‘If you do it right, then it’s great. If you don’t have the right stuff in place, you just blow it,’ shares Biz. ‘Don’t turn on the tools of the trade for growth until you have a system to capture and make use of that growth.’