Have you ever seen a plane above you and wondered where it is coming from or where it is going to? Well, over Scandinavia you can actually get that info for quite a lot of the planes that you seen in the sky.  Check out flygradar.nu and click on the various planes to get more information about the flights. It is not really a radar as far as I understand but a radio signal (Mode-S/ADS-B-transpoder) that most modern planes have and it seems like it gives the position of the plane pretty accurate. Thanks to DinSide for reminding me again about this web site