APRS Air Mobile
Running APRS while flying is a fun and semi-useful project. APRS often has much better aerial coverage than cellular networks, allowing friends and family to see your location as you fly across the country. And yes ADSB does this too but practically, only if you have a 1090 (mode S) ADSB solution. The UAT solutions I have do not have much coverage on sites like flightaware due to fewer 978 ground receivers and the fact that the airborn transmitter is very low power (fractions of a watt vs hundreds of watts for a mode S transponder).