Idependet developed games are games developed without major software producer backing or support. Most games are freeware or shareware.
Flight Gear
Taken from the official site.The Flight Gear Flight Simulator project is a free, open-source, multi-platform, cooperative flight sim development project.
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Flight Sim Toolkit
Flight Sim Toolkit is a complete set of graphical tools for making completely original flight simulations.
OpenFly,
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