"We've all built these giant personal networks," Stone told this newspaper, "but what's the true promise of a connected society? It's got to be to help each other."
Stone, 39, said he'd begun noodling on his next act shortly after leaving Twitter in mid-2011. He has already turned much of his time and wealth to philanthropy, but with Jelly, he hit on a more immediate question: "What if you had to build a way to get an answer?"
Available on Android and iOS, the app aims to harness the wisdom of a user's social networks to answer questions about most anything that you can photograph with a smartphone. Say you're on a hike and don't recognize the wildflowers -- take a picture of the landscape, zoom, crop or use your finger to draw on the flowers in question, and post to the site to ask your social networks for an answer.
While websites like Quora have taken off in recent years to help users get questions answered, Stone says he focused on photos and location -- "the things that make mobile mobile'' -- to help users get real-world answers fast.
"We're not asking, 'What's it like to be in jail for 20 years?'" he said in a gentle dig at some of the philosophical meanderings of many Quora users. "It's, 'How do I set up my TiVo? Here's the back of my TV.'"
Stone kept his latest project mostly under wraps until November, when, on the same week that Twitter began trading publicly on the New York Stock Exchange, Jelly quietly announced itself with a new website, jelly.co, and office in San Francisco.
The company is a confluence of the brains and fortunes of the Twitter inventors, who helped wrangle the backing of a celebrity-studded lineup of investors. The list includes the likes of Bono, Al Gore and LinkedIn co-founder Reid Hoffman.
"Success breeds success," said Brian Blau, a consumer technology analyst for Gartner. "When you're on a roll and you have good ideas, you have the resources, you have the experience, and you have the connections to the technology community."
Stone has had his fingers in a number of projects by Twitter's other co-founders. He helped launch Medium, a storytelling platform that former Twitter CEO Evan Williams mostly runs. Stone also helped Jason Goldman, vice president of product at Twitter, with Branch, a website for public debate. Medium, Branch and Jelly were all started at Obvious, a startup incubator and investment vehicle the three tech leaders created.
And Twitter co-founder Jack Dorsey, who runs San Francisco-based payments company Square, joined Twitter investor Greg Yaitanes and Williams to help fund Jelly.
"Jack was like 'This isn't just a good idea,'" Stone recounted. 'It's something uniquely suited to you.'''
Contact Heather Somerville at 510-208-6413. Follow her at Twitter.com/heathersomervil.