NoMachine essentially made themselves irrelevant by not upgrading their client software often enough, IMHO. I was using all sorts of VNC hackery to make it fast and loved NX, but it was weird and niche (never worked quite right on the Mac) and still slow when compared to RDP and Citrix, so the rise of Ansible and other sorts of automation blew it out of the water for server management.

For end-users, Citrix was just way better, even if more expensive, and there was no compelling reason to switch...

I use x2go actively for all my servers. It is very fast, even over slow connections (much better performance then VNC and RDP used to have) -- thanks to great compression techniques (so do not expect 256 colours when connecting over GSM network). It is a lovely piece of (OSS!) software.

Nice to hear it's working well.

I found out today that X2Go version 4.1 is available on Debian Stretch via "backports"; I don't need it at the moment but if I'm bored in the future, I could play with it without much friction...

Can Nomachine/X2go run a server on a windows machine?

X2Go shouldn't work, unless you intend to run it on a VM or maybe the WSL as it's a modified Xorg X11 server, but probably it's not what you are asking.

NoMachine, according to their download page, should support Windos/Mac/Linux on the server front, but I don't have a direct experience.

NoMachine runs on a Windows server. It accesses the remote desktop. But if what you want is a Terminal Server like NoMachine's Terminal Server for Linux, I think you'll be disappointed. That's not possible from a legal perspective.

Ten years ago, UltraVNC or RDP were the fastest remote desktop options for Windows. I also can recommend TeamViewer, despite it has a slightly different focus.

I used it until a few month ago: it worked better (lower latency and no need to specify the resolution) than VNC but clion doesn't work well with NX, so I switched to VNC.