How Do Airlines And Charter Operators Track Their Fleet?

[Jettly]

With maintenance issues and things happening always on the fly with little warning, what systems are used by airlines and charter operators to track the status and whereabouts of aircraft to help the charter operators best plan and position their aircraft?

Obviously I understand it would be gps based but what software handles all of this and does it tie in to the aircrafts onboard GPS some how?

Thanks!!