Facebook has a problem: How to get its 500 million users moving?

The popular social network has about a half billion users, yet Facebook doesn't have a single, unified version of its mobile site -- yet. That all changed Wednesday at a special event at Facebook headquarters, where company head Mark Zuckerberg unveiled a new mobile platform. 

But no Facebook phone.

"There's been a rumor floating around that Facebook was going to build a phone," Zuckerberg joked. "No," he said simply. But the company did need a way to simplify development for the 200 million people who use its social network on various mobile devices. 

"The only platform bigger than this is the mobile web itself," Zuckerberg told attendees at the event. So he unveiled a new mobile platform including a unified, single sign-on feature, and new tools that the company claims will encourage developers to build better apps.

But no Facebook phone.

A number of developers came on stage to show off new apps that incorporate the new software, built with a new SDK -- or software development kit, the tools a programmer uses to write software -- which Facebook announced would be released shortly. Part of the SDK is a set of tools specific to mobile application developers. One is the single sign-on feature, which lets users sign in to Facebook simply by clicking a button, rather than entering their user info.

But no Facebook phone.

Prior to the event, rumors swirled about what would be announced at the mobile event, rumors centering on a potential phone. The invitation Facebook sent provided no details whatsoever other than to say that the event begins at 10:30 a.m. on November 3 and would be followed by lunch.

But the invitation sported an image of two shaded figures alongside what appears to be the old string-and-Dixie-cup phones that kids in treehouses have long used to communicate. One hopes an actual Facebook phone -- if it ever arrives -- will be slightly more high-tech.

Technology blog TechCrunch reported last month that Facebook was secretly developing a special smartphone.

Facebook then issued a carefully-worded response that said the company was not “building” a phone. The company had projects focused on “deeper integration with some manufacturers.”

But to be clear: There's no Facebook phone.

Jeremy A. Kaplan is Science and Technology editor at FoxNews.com, where he heads up coverage of gadgets, the online world, space travel, nature, the environment, and more. Prior to joining Fox, he was executive editor of PC Magazine, co-host of the Fastest Geek competition, and a founding editor of GoodCleanTech.