The FlightGear flight simulator project is an open-source, multi-platform, cooperative flight simulator development project. It also simulates space flight in Earth's orbit.
FlightGear's flight dynamics engine (JSBSim) is used in a 2015 NASA benchmark to judge new simulation code to the standards of the space industry. It's used professionally for research and development as well as non-professionally.
Tours of real locations inside the game.
FlightGear 2020.3.8 and later has 3d models of buildings, roads, cities etc. , based on Open Streetmap (OSM) data and automatic generation, for the whole world.
SpecsUpdate
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Pros
Pro Worldwide scenery
FlightGear has scenery that contains environments to fly in from the whole globe.
Pro Free and Open Source
All code written for FlightGear is opensource and available for anyone to use.
Pro Crash animations in some aircrafts
Pro It has world-wide multiplayer
Pro Live cockpit
Pro A lot of aircrafts to add
Pro It has amazing graphics
Pro You can almost recreate real incidents
Pro No bugs
Cons
Con Not as graphically advanced as commercial competition
Con Getting stuck upside down
After a crash a pilot may be stuck in an upside down position with no way to recover.