This app was mentioned in 2 comments, with an average of 1.00 upvote
It's also a web client, but it's also a desktop client for windows.
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For Android you can install the emby tv app, which is closer to theater than to the web client: https://play.google.com/store/apps/details?id=tv.emby.embyatv
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It's still rather ugly though - especially with that big fat bar on the left.
I've bought and buying more ShieldTVs (16GB versions and then buying large microsd cards) to replace all my Boxee Boxes. I'm using a HDHomeRun Connect to replace the Boxee USB TV dongles and have Chrome and Firefox browsers installed on the ShieldTVs which sync to the PCs configurations.
Although I do have a USB 3.0 portable drive hanging off one of my ShieldTV to store video to watch when on travel, I have all my media on large NAS units. I've installed Emby, since Plex doesn't support the DVD and Bluray ISO files I was playing on the Boxee Box.
How to install Amazon Prime Video on the ShieldTV, I've been using this method for quite awhile, not 4K but I can live with that until an official app is released.