VNC is one of popular thin client computing systems, which supports cross-platform remote control using the RFB protocol. Unfortunately, since VNC does not provide functions specially designed for collaboration, it is difficult to collaborate effectively through the remote control function of VNC. In this paper, we present the extension of the UltraVNC server and the JavaViewer client which are one of open-source VNC systems. For effective real-time collaboration, the extended VNC provides three kinds of access authorities to control the collaboration server: administrator, worker, and spectator. The administrator can control the access authorities of the users through the access control tool, newly provided in the extended JavaViewer. The workers can access the resources of the remote server, whereas the spectator cannot handle those remote resources, only monitoring the remote server. In addition, the extended VNC provides the one-click connection facility for easy connection to the collaboration server from many collaboration participants.