There’s a cross-platform flight simulator called X-Plane which is quite competitive with the well known MS Flight Simulator. It’s extensively modifiable, playable over networks, and has an amazing amount of third-party material available.
Today I found the VF-1 Valkyrie file! Custom cockpit, swing wings, and even details like gear doors and vectored nozzles operating perfectly. It doesn’t transform, but that would be asking a lot. And you can even fly it over the deserts of Mars! There’s a nice movie of the fighter running in X-Plane too.
There’s also files for the Space Shuttle, the Marine Dropship from Aliens, and somewhere (haven’t found a link yet) Thunderbirds 2 and 3.