Remote Desktop
Tiger VNC
Nixpkgs has a package but no service.
The server component can be started using the vncserver command.
To connect use the vncviewer command.
x2go
X2go packaged in nixos as x2goclient.
RDP
NixOS has first class support for XRDP server.
services.xrdp.enable = true;
services.xrdp.defaultWindowManager = "${pkgs.icewm}/bin/icewm";
networking.firewall.allowedTCPPorts = [ 3389 ];
freerdp or remmina can be used on the client side.
Guacamole
Not yet added to nixpkgs