Plex is based on xbmc, but has moved to a client/server model.
server runs on all the basics..
linux, mac, windows, and some NAS devices
client runs on...
ios, android, windows, mac, linux, some smart TVs, roku, and with an easy tweak replaces the trailers app on your apple TV. and there's a dedicated RasPi distro that runs it
it's nice in that you can watch a show, stop in the middle, change rooms/clients and pick up right where you left off.
if the media file is not compatible with your client, then the server will convert on the fly to something your player can handle, even taking DTS 5.1 to dolby digital if needed.
(this does mean you need a server with a decent processor if you have a lot of incompatible files)