"VNC was originally developed at the Olivetti Research Laboratory in Cambridge, England. Which was then owned by Olivetti and Oracle Corporation. In 1999 AT&T acquired the lab, and in 2002 closed down the lab's research efforts. The original VNC source code and many modern derivatives are open source under the GNU General Public License." - wikipedia
There are many, many types of VNC programs. You are requesting RealVNC, but there is also TightVNC, UltraVNC, Chicken of the VNC, ChromiVNC, PalmVNC, WinVNC, Helpdesk VNC, OSX VNC, Apple Remote Desktop, x11vnc and likely many more.
Any reason you need REALVNC over an older version of say TightVNC, which is free.