The library provides for simple rfb-protocol based control of a VNC server. This can be used, eg, to automate applications (sometimes there is no better way), or script some sort of interaction. Being VNC based gives it the advantage of being able to be run against servers on any platform.
# launch xclock on localhost. note that there is an xterm in the top-left Net::VNC.open 'localhost:0', :shared => true, :password => 'mypass' do |vnc| vnc.pointer_move 10, 10 vnc.type 'xclock' vnc.key_press :return end