Plane Tracker

Flight tracker apps are slow, complicated, not very intuitive, bloated and add-riddled. Plane Tracker is simple, lightweight and good-looking.

It’s free, has no ads, looks great, lets you set trips with multiple flights. This app is open-source. 

Note: This app had to be taken down from the Play Store, as the API that it uses is sadly no longer free to use, you can read more about that here.