Flightradar24 is a commercial, real-time airplane tracker. The application costs $6.99 if you want to use the desktop version, but you can access it for free on your web browser.
What Flightradar24 basically does is show you the locations of airplanes on a satellite map. It can't track every single aircraft that is on the air. In fact, it can only track aircraft that have an ADS-B transponder equipped. So, you won't be able to see any traffic at all in some countries, and just some traffic in others. In the case of the United States and Europe, you will see lots of planes moving around, but keep in mind that not all of them are seen. The planes are represented by a yellow image of a plane. The image moves following the current position of the plane. You can zoom in and out of the plane, and in some cases, when you click on planes, you will see some information about them. For example, one of the planes that I clicked on was RAM663R. A new pane popped-up, which showed a picture of the airplane, along with information such as company the plane belongs to, destination and origin, aircraft type, registration, altitude and more.
In short, Flightradar24 is a nice application that lets you track some aircraft in real-time, from the comfort of your desktop. It even lets you access information about them. When all the traffic can be tracked, I will getting this for sure.