NICE DCV is a good alternative if you don't mind paying. I've found the image quality, latency and multi-monitor support to be better than NoMachine. You can get a permanent licence for $180.
They are owned by Amazon Web Services.
They are owned by Amazon Web Services.
There's also RustDesk that looks great but I can't say I've used it yet.
I’ve found NICE DCV to be more performant on low end clients (eg chromebooks) maintaining good responsiveness vs RDP.