RealVNC (formerly winVNC)
Real VNC
Use it to remotely connect to other computers and manage them as if you were at the terminal. The free copy does not include encrypted connection channels or file transfer, but I found that to be a moot point because I generally used it for computers that didn't have monitor/kb/mouse on my network.
It's the ultimate choice in high school teenagers' remote counter-strike server management...man those were some good days. I feel old now.