Moonlight as a protocol is quite cool, made for streaming games in fact. Sunshine is a open source server implementation, and the client was open source to begin with, I think. Sunshine is multi-platform, and so is Moonlight the client. I used it to stream my Linux desktop (and games) to my Android phone.

I also have good experience with Spice. I haven't found a way to set it up as a server, but Qemu uses it for all its VMs, and the performance is great, you can watch videos and everything, if you have the bandwidth.

For WiFi and slower networks, Moonlight was way more performant for me.