Flighter
For the person meeting someone at arrivals, not for someone watching aviation.
Flighter is being built. This page describes what it will do; the code is private while it is written, and there is nothing to download yet.
When it ships it will be on Google Play and in the self-hosted F-Droid repository that serves every app here — two builds, signed by different keys, so Android treats them as separate apps and moving between them means uninstalling first.