Today Tumblr is making its debut in the social app space for mobile platforms. Its entrant is called Cabana, and basically it's an app that lets you watch the same video together with your friends in real time.
You hang out with up to six friends in a "room" inside Cabana, where you share videos from YouTube (other sources may be included in the future). You watch these together with your friends, in sync and in real time. While that's going on, you also video chat with your buddies, and your faces are all there in the app's screen. This, Tumblr staff says, really recreates "the experience of being together while you're apart".
Any person in a room can pause and change what's being watched, and you can only be in one room at a time. That said, you can leave and re-join rooms as you see fit. If you switch to some other app on your phone while a video is playing, you will be "put on pause".
Cabana is available now for iOS, and will be out for Android in May.