FlightCode lists ICAO and IATA Codes for airports, aircraft types and airlines. It also lists the country codes/registration informations of an aircraft.
You'll find a link to the maps application for many of the listed airports. And you can mark everything you've seen (spotting function). Stay in touch with the developer by using the direct feedback and bring in your ideas to make this application better and better. Nice photographs draw a better picture of the topic. Enjoy flying and enjoy FlightCode!

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For passengers:

You want to know where the nicely colored aircraft comes from? Look at the country codes of FlightCode.
You want to look where on your route the fuel stop is, but you only have shortcuts on your tickets? Look at the IATA airport codes in FlightCode.
You like to know what the shortcuts on your luggage labels tell you? Or you just want to look in the FlightCode database when you don't have internet access during the flight?

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For Pros:

You only have IATA Codes on your flight schedule and want to know what the new destination on that plan is?
You got smaller airports on your route, on the left and on the right, and don't want to consult the manual? The offline database of FlightCode can help.
You recognize a callsign like "Yellow Flyer" in an aircraft radio call? Look up the ICAO Callsigns with FlightCode to know what Airline this is...

Note that this app has its focus on IATA and ICAO standards and does not yet include the full list of FAA airport codes (which is planned for a future release).