Remote Desktop
Tiger VNC
Nixpkgs has a server package but no service.
x2go
...
RDP
NixOS has first class support for XRDP server.
services.xrdp.enable = true:
services.xrdp.defaultWindowManager = "${pkgs.icewm}/bin/icewm";
networking.firewall.allowedTCPPorts = [ 3389 ];
Guacamole
Not yet added to nixpkgs