Flightradar24 shows live airplane traffic from all around the world. The technique they use to receive the flight information is called ADS-B. Which means they can only show information about aircraft equipped with an ADS-B transponder which about 60% (about 30% in USA and about 70% in Europe) of the passenger aircraft have (here’s a list of plane types). The reason you don’t see a ton of planes all over the world is because Flightradar24 only has a network of about 500 ADS-B receivers and 90% of them are in Europe. It’s still cool and users can change the view to either: map, grayscale or satellite images and jump to any area of the world by using the drop down menu on the upper right. You can also click on any aircraft to get specifics such as the: airline, flight number, departure and arrival cities, type of aircraft, registration number, hex, altitude, speed, track, squawk, position, and radar type.