I'm looking for a replacement for a custom vnc server that we have been using in my company for a long time. I need a simple executable that can be run from command line by an IT Support software without the user noticing it (our application will warn the user, we don't want him to see we are using that VNC sever).

I need it to support Windows and preferably also OSX. The only option I've found is UltraVNC, but I can't configure it from command line to accept loopback connections without authentication.

We have already a whole VNC Viewer + VNC Repeater + Bouncers architecture, and the only missing piece is the VNC Server.

Do you know any solution you could suggest me? I'm afraid I'll end up developing a new VNC server myself, may be based on an open source one.

EDIT: When I said I don't want the user to notice this VNC server, I should have added that I don't want him even noticing the installation. So better if it can be installed silently or can be executed as a portable executalbe (for instance, ultravnc can be installed and ran as a service from command line, or simply executed quietly, with only a notification icon; its problem is that I can't run it without authentication).