No Machine floating window
No Machine can proxy a rootless X11 session by setting the Floating Window option in the custom session settings.
This allows you to run, for example, a remote xterm on your desktop.
"So what's so great about this," you may be wondering, "compared with running my own X11 server and forwarding the connection over SSH?" The answer is speed. The No Machine proxy protocol makes this much much much much faster than plain X11 forwarding. Select the Disable X agent encoding and you effectively are just SSH-forwarding the connection. See the speed difference for yourself!
Of course this is a proper rootless environment and you are not limited to just one Floating Window. Any new windows opened in your session will be handled correctly.