ProFlightSimulator: Commercial FlightGear Fork (Weak)
ProFlightSimulator ad on Free Gamer
A reader pointed out a hilarious coincidence: an ad of ProFlightSimulator, a fork of FlightGear on top of the Ripping-off open engine games post.
ProFlightSimulator is an open source stand alone Flight Simulator. As always disclosed this is a split / branch from the FlightGear community and has been set up for a very specific reason. It's different from FG due to the many major changes to the game.This info is placed in Disclaimer/Terms/IsThisFlightgear?.
The text "Source code available in members area" is part of a background image in the footer of their homepage. There is also a .7z file containing "Source code of these images, content and files" (244MB - For a list of the file's content see here).
Why PFS is not FlightGear
The FlightGear team is aware of the for-pay forks and wrote a FlightGear-Professional explanation of the situation.
I have an ethical problem with there not being a "for every (final) purchase, we donate $1 to the FlightGear project" commitment. Maybe the improvements/code changes are at least useful to the FlightGear project, if any of the devs went through the trouble of buying PFS.