Sivan has brought us another great tool... from his email to me:
"NXTender is a Windows program that allows your NXT to control your PC. It allows the NXT to send keyboard keyclicks to the PC (simulating a keyboard), to open windows and display data in them, and to receive joystick input from the PC. When you use NXTender, you normally program only the NXT brick. The NXTender runs on the PC and does not require programming. Bluetooth messages from the NXTtell the PC what to do, when to send data back, where to send it, what to display on the screen, etc.
Additional functionality can be added to NXTender via relatively-simple plugins that are implemented in Java. That is, the standard version of NXTender does not allow your NXT to control your USB cup warmer, but if you know a little bit of Java and you know how to control that cup warmer from a PC program, then you can write a NXTender plugin that will give your NXT conrol of the cup warmer.
Finally, a challenge. NXTender allows you to build a Lego mouse-type device for your PC without any PC-side programming. Try to build a good one.
Check it out here.