Today NATS (UK ATC agency) brought out an app. It’s called Airspace Explorer:
Basically, It’s FR24, from an ATC point of view. Aircraft have really detailed info, including altitude, airspeed, distances, registration, plus aircraft specifics such as height and wingspan. It also has a 3D view, which puts the aircraft at their various altitudes at scale, so you can see climbs and various levels.
Even cooler is the ATC features- the app allows you to see airspaces, FIRs, UK airways, and other awesome stuff.
It’s free, just available for iPad ATM. If you have an iPad, get this. It’s incredible.