I like FlightAware or Flightradar24. Both are free apps, but you can also pay to upgrade to premium membership with additional information (like age of plane). FlightAware is the gold standard in my opinion. You can track heading, altitude, speed, time to destination and more. I really like the feature “Where is my aircraft now?” You can track your inbound flight to see when it’s going to land. Comes in handy when the airline won’t give you solid information on why you’re flight is being delayed. You can literally see where your plane is at and know for yourself it’s stuck in the ground in XYZ, or 20-minutes from landing.