Unlike it's recent foray into photo filters, Vine is not a feature baked into the standard Twitter client. Instead, the service can be used either independently or in collusion with Twitter. Users can link Vine with their Twitter account via a common login or they can create a new account entirely. The app can find friends who also use Vine by accessing your Twitter account, Facebook, or contact list.
Vine represents Twitter's efforts to move beyond simple posts of 140 characters or less and develop a versatile media platform of its own. The app is available for free now via iTunes for iPod touch and iPhone with other platforms to follow.