Free Remote Control/Virtual Network Control (VNC) Software are thoses tools which allows you to view another computer's desktop on your own computer via a network. You can use the remote desktop as if you were sitting before it.
These software can be useful to perform maintainance jobs on the remote computer. Usually, you just need to install a software on the remote computer, also known as the server and another piece of software on the destination computer (yours) known as the client.
This way, you can diagnose the computer without the need ti travel to the place where the computer is.
UltraVNC - Free Remote Control/Virtual Network Control Software
This software enables you to access a remote computer and use your mouse and keyboard to interact with its desktop. You can perform file transfers and chat with the person who is with the remote computer. You can run this program through a network or simply the internet. You can also view the desktop though multiple monitors if the remote computer is running on multiple ones. You can also protect your data stream between the two computers from being intercepted by encrypting it. The software provides a video driver which speeds up the viewing of the desktop significantly and UltraVNC also has an auto-reconnect feature which restablishes the connection if the latter is disrupted. This software works on Windows. Recommended!
TightVNC - Free Remote Control/Virtual Network Control Software
This software allows you to establish a connection between two computer to allow to to view the desktop of the server computer. You need to have an internet connection to be able to establish the connection. You can transfer files among other things and encrypt your data stream. The software, like with UltraVNC, compes with a video driver which speeds up rendering of remote desktop on your computer. This software is released under the GNU GPL License and runs under Windows and Linux and other types of Unix OSes.
Chicken of the VNC - Free Remote Control/Virtual Network Control Software
This software is a remote desktop control software for MAC OS X, It allows you to display the reomte desktop and interact with it like you were sitting before the computer. You use your mouse and keyboard to control the remote computer. This software is released under the GNU GPL License.
CoRD - Free Remote Control/Virtual Network Control Software
This software allows remote connection between MAC OS X and Windows computers. You can view the Windows desktop as if you were before it and you can interact with it. The only way of transferring data between the two computers is by the clipboard function present in CoRD.