For the sufficiently geeky aviation nerd there’s FlightAware, a website that tracks just about every airliner and most private planes currently in flight. The folks at FlightAware compile all the information with the help of a few thousand volunteers around the world that have a bit of hardware to listen to ADS-B transmissions and relay them to the FlightAware servers. Now you can do this with a Raspberry Pi, and as a nice little bonus FlightAware is giving away free enterprise accounts to anyone who does.
Listening in on ADS-B transponders is something Raspberry Pis have been doing for a while, but doing anything useful with the altitude, speed, heading, and registry numbers of various planes flying overhead is pretty much FlightAware’s only reason for existing, and the reason they’ve developed an easy to use software package for the Pi.
Setting everything up requires getting dump1090 running on the Pi, the only hardware required being an RTL-SDR USB TV tuner, a GPS module, and an antenna for 1090 MHz. From there, just send all the data to FlightAware and you get a free enterprise account with them. Not a bad deal for the aviation nerds out there.