FlightGear is a flight-simulator created by an international group of
volunteers, and released as free, open-source GPL software.
It has been used for academic research, education, and for fun.

To build the internal Qt launcher, you will require QT5 and then pass
QT5=yes to the script.  Otherwise, you can install either fgo or ffgo
as a more basic launcher.

speex and flite are optional dependencies for voice communication
(autodetected at build time).