Radmin Viewer is the one of the most famous remote administration tools on the market today. This is because of its affordable price and high scalability. Moreover, the application has an address book feature, so you can add data about multiple computers and group them into folders.
The basic function of this program is to enable you to remotely control another computer's desktop, so any mouse click or keyboard strike will be transferred over to the other program. This will enable you to install applications, fix technical problems, and much more.
One of the great features of this application, which you cannot easily find in other tools of the kind, is the ability to do voice and text chat with the person using the computer being controlled remotely. Another awesome feature is the ability to transfer files to and from the other computer without the need of any additional tools.
One drawback that I found in this program is the lack of ability to connect to a computer outside the local network in case that it's behind a firewall / NAT. Competitive applications like TeamViewer can easily connect to any computer running the server application even if it doesn't have a real IP.