UNLICENSED GAME This game is an unlicensed version of Microsoft Flight Simulator X. User Summary Prepar3D is Lockheed Martin's continuation of the Microsoft Flight Simulator family of games. It is based on the Microsoft ESP simulator, which is the commercial-user version of Microsoft Flight Simulator X. While Prepar3D is fully licensed and authorized by Microsoft, the limitations of that license prevent it being sold for "personal computer entertainment". It is however seen by many members of the flight sim community as the natural continuation of the series, and the licensing constraints that it is sold under are not seen as a limitation to the end user.