A comparative list of remote desktop software can be found here: Comparison of remote desktop software
Remote control is possible in two modes:
The software on the controlling computer transmits its own keyboard and mouse activity to the controlled computer, where the remote control software implements these actions. The controlled computer then behaves as if the actions were performed directly at that computer.
The duplicate desktop mode is useful for user support and education. Remote control software combined with telephone communication can be as helpful for novice computer-users as if the assistant was actually there.
Typical commercial programs used for controlling Windows PCs include NetSupport Manager, pcAnywhere and Laplink. For Macintosh computers, there is Apple Remote Desktop and Timbuktu (Timbuktu also works under Windows). There is also open source remote control software such as VNC (which stands for Virtual Network Computing) and FreeNX.
Another solution is a Web control, you can use your computer anywhere and any platform, is a FogCreek-like solution.
It can also be used for "headless computers". Instead of having separate monitors and keyboards for each computer, or using a KVM switch, one can attach a single monitor, keyboard and mouse to one computer with remote control software, and use it for operating the other computers.
In this case the controlling computer will work almost the same as on a duplicate desktop, except that the actions of the controlling computer may be almost unnoticeable on the remote computer display. This way several people can use the same computer at once, without disturbing each others work.
This could be useful for several administrators doing different tasks on the same server. It can also be used for using hardware attached to the controlled computer, without disturbing a person who may already be using the computer.
If the controlled computer is powerful compared to the controlling computer, it can feel as if the controlling computer is a better computer. The controlling computer only need to be powerful enough to run the remote controlling software, therefore it can be a very simple and cheap computer. When one uses such a "thin client" or "dumb terminal", they may not even know that their software is actually running on another computer.
In some cases it is cheaper to buy one large computer, and several thin clients or dumb terminals, than purchasing a complete computer for each workstation. If one already has enough computers, but they are not powerful enough, only one new computer may be needed, and the old ones used as thin clients.
The amenities of modem remote-control software made accessible to Windows users. (Norton-Lambert Corp.'s Close-Up 4.0) (Now in the Channel) (Product Announcement)
Dec 01, 1991; The convenience of modem remote-control software just got a little more accommodating. Although the DOS world has enjoyed the...
Get closer to your computer ... from afar. (Software Review) (overview of five evaluations of remote control software packages for the PC and one for the Macintosh) (Evaluation)
Mar 01, 1992; Remote-control software lets you dial up a distant computer and use it (almost) as if you were sitting right there. It will let...