http://www.prepar3d.comIt's a recent simulator based on ESP ( FSX for the professional market ), that has been made by Lockheed Martin after buying the ESP license from Microsoft. It has an updated graphic engine based on DX11, with new features like dynamic shadows, cloud shadows, etc.
Since it's more or less backward-compatible with FSX, requiring just some tweaks to the sceneries and the installers, we support it as an alternative to FSX. You can install all our products under P3D, without requiring a separate license.