While UltraVNC is aimed only at Windows computers, it has pioneered and perfected features that the other flavors have consistently refused or been very slow to implement for cross platform and minimalist reasons.
This is the recommended VNC flavor for use with VNCScan.
This is also the official website for the original VNC. Their free version is very limited but they have a commercial pay version that has some of the UltraVNC features.
TightVNC is a heavily modified version of the original VNC 3 server and client. It has added features such as file transfer, performance improvements, and read-only password support. They have just recently included a video drive much like UltraVNC's.
OSX VNC is the VNC client/server for Macs. There is also a version for OS 9 on their website. I am working on a way to deploy the OSX version with VNCScan.
Notable VNC Links
This is the home of the FastPush deployment script. VNCScan uses a modified version of this script.