Plex is a media streaming app that is available on your Windows Phone and Windows 8.1 device. But it is missing from the Microsoft hardware where it is perhaps most useful - the Xbox One.
This is about to change. Plex is undergoing testing for the Xbox One and there are already screenshots on the Xbox servers. The app has been in development from April, and hopefully, is near completion.
Plex is a system to store your media (pictures, videos, music, movies) through their Media server, which you can then watch through the Plex apps on all your devices. If you have lots of movies on your laptop, and wish you could watch them on your tablet, smartphone, TV, etc., you are the target audience. In addition to playback, Plex offers organizational tools and conveniences such as starting media from where you left off on another device.
You can get started here. Also note: this is a paid service.