UltraVNC is based on VNC and has an edition that is free. It works well in service-mode with Windows 7 (being able to control both desktop and UAC dialog box). User-Mode only controls the desktop and will not show the UAC dialog on the viewer machine if it appears on the server machine.
One thing we like about UltraVNC (free edition) is its capability to chat and transfer files. They also have a single-click version which allows our client to download from our site and be able to instantly connect with us for remote assistance.
We were also happy with RealVNC. Unfortunately, in most UltraVNC Server installations on Windows 7 or Vista (both User-Mode and Service-Mode), RealVNC could not connect properly. RealVNC is fast and stable on Windows XP compared to UltraVNC on default settings (Full colors). Changing UltraVNC to 64 colors (the default of RealVNC), UltraVNC can be as fast and stable as RealVNC.
If RealVNC fixed the Windows 7 Aero and UAC problems, we probably would have stayed with RealVNC. Support for both is still on going and the competition between the two would eventually lead to better implementations of VNC.
