VNC Development Library
VNC is a set of programs using the RFB (Remote Frame Buffer) protocol. They are designed to "export" a frame buffer via the network. It is already in wide use for administration, but it is not that easy to program a server yourself. This has been changed by LibVNCServer. X.org already has a virtual Xvnc server which you can start as an own screen (e.g. :1) and connect to with a VNC client (e.g. vncviewer from tightvnc). The x11vnc binary (that allows you to export the window of a real running X11 server) has been split off into its own package on 2007-07-16.