Google Earth VR - Walk the earth in VR
X-Plane - The world's most advanced flight simulator just got an upgrade. Download the free demo today for Windows, macOS, & Linux.
Lonely Mountains: Downhill - Take your bike and find your own path down mountains.
FlightGear - 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. It's flight dynamics engine (JSBSim) is used in a 2015 NASA benchmark.
Nice Trails - Turn GPS tracks into 3D printed mountains
Digital Combat Simulator - Digital Combat Simulator is a Free-to-play, Single and Multiplayer Combat Flight Simulation developed by Eagle Dynamics and published by The Fighter Collection.