It appears to be a complete machine image for the Pi: "Pex Media Player for embedded devices is a small Linux based operating system that turns your Raspberry Pi 2 or Intel HTPC into a dedicated media playback device."
If you looking for the Raspberry Pi 2 downloads or the x86 download for Embedded Device you need to sign into your plex pass account first, then theres a button on the downloads page called "Plex Pass Downloads"
It seems as its a beta its only open to plex pass subscribers.
It's Taken me 30minutes to work this out (luckily I am a subscriber)
That is the RasPi port of Plex Home Theater -- the previous player which is no longer being developed.
"Is Plex Home Theater still around? Plex Home Theater is still available and open source. We’re no longer actively developing it and are focusing our efforts on making Plex Media Player the best experience possible. (We’ll continue to make bug fixes for PHT for now.)"
