Actually Haiku has a very good remote desktop system in the app_server and there was even an HTML5 client though maybe right now it is quite stale. I don’t think much of this is well documented, it is something I wanted to dive into the next chance I have for serious Haiku development, which might be soon…
Edit: Here is an article on it, though it is pretty old I think and doesn’t have a ton of detail: Using the remote app server | Haiku Project
Also some of the limitations sound a bit annoying, like not being able to have the same app on each “screen”.