VNC server to allow remote access to an existing X session

 x11vnc allows one to view remotely and interact with real X displays (i.e. a
 display corresponding to a physical monitor, keyboard, and mouse) with any
 VNC viewer. It has built-in SSL encryption and authentication, UNIX account
 and password support, server-side scaling, single port HTTPS and VNC, mDNS
 service advertising, and TightVNC and UltraVNC file-transfer.