UltraVNC is a remote access program that allows you to securely access another computer. This application is clearly geared more toward people with an advanced knowledge of computers and remote access. If you've never set up this type of connection before, it could be a bit overwhelming, but if you're used to the terminology and settings required for setting up remote access, you should find this app quite powerful.
Dual installation: When you download the install file, you end up installing both the server and the viewer application on the computer. This means that your computer can both access computers remotely, and be viewed remotely. This helps makes installation of the required software pretty straightforward, before you start trying to access a system.
Chat system: The chat system works very well. If you use this application to help someone else troubleshoot some sort of problem on their computer, which is a very common use of this type of program, the chat feature lets you easily converse with them directly. This is very useful when trying to resolve complicated problems that require some help from the other end of the connection.
Intimidating interface: When you first log in into UltraVNC, it can be very intimidating. If you don't know what you're doing, you will be confronted with a lot of complex settings and options that won't mean much to you, and there isn't any real indication built in-app to help you understand how to use it in a straightforward manner.
Windows only: Since this program is a Windows-only application, it may reduce the number of people you can work with.
If you're well versed in remote connections and need to work in a Windows-only environment, UltraVNC could be a very useful app. It is relatively easy to set up, and has a great chat feature that allows for clear communication with whoever is on the other end of the connection.