Twitter's video-sharing app, Vine, is now the top free app in the iOS App Store. Released back in January, Vine was well-received by the press and has been the most-downloaded app in the "Social Networking" category many times. In the two-and-a-half months since its release, it has slowly climbed the overall US "free app" charts before reaching number one yesterday. Vine co-founder Rus Yusupov announced the milestone in a tweet claiming Vine is now "the number one most popular app in the world" (it's not).

While there's been no advertising campaign to promote the app, tight integration has meant that Twitter users not familiar with Vine are often exposed to the short clips. The app has also been promoted heavily on the App Store as a "featured app." Vine's popularity is certainly impressive, especially when compared to some of Google's and Facebook's attempts at standalone apps like Facebook Camera and Google Field Trip. Getting the app onto phones is only one half of Twitter's job here, though, and the company hasn't given out solid figures for how many people are actually using Vine.