iOS: Vine is a free app for iOS that allows you to shoot short videos and share them with friends. The service integrates tightly with Twitter, partially because Vine was acquired by the company today.
Vine is a free app and free service, and while the company is partnered with Twitter, you don't need a Twitter account to use it. Just grab the mobile app and start shooting. You are restricted to short videos -- six seconds or less -- but once you've stopped recording, Vine creates a loop of the video and gets it ready for your friends to see.
From there, it's a single tap to get the video up on Facebook or Twitter -- where people can see the video embedded in your tweet. Check out this example or this one to see what the app can do. Hit the link below to learn more, or grab the app from the iTunes App Store to try it out.