It's a remarkable thing. FSX shipped during the Bush administration. It predates the iPhone. Microsoft has released four newer flight simulators since (Flight, FSX:Steam Edition, MSFS 2020, MSFS 2024) — and FSX still has the most active mod community of all of them.
Part of that is inertia. Twenty years of freeware adds up. Most of the world's GA aircraft, every commercial airliner you can think of, scenery for nearly every airport on earth — if you can imagine it, someone has built it for FSX. The other part is the platform itself. FSX is forgiving. It runs on modest hardware. Its file structure is simple enough that a hobbyist with no programming background can edit aircraft.cfg by hand. There's a low barrier to entry for both flying AND creating.
The Prepar3D crossover is the other big factor. P3D inherited FSX's plugin architecture, so the same aircraft, scenery, and AFCAD files mostly drop straight in. That doubles the addressable audience and keeps the development pipeline alive.
What you'll find in this section: thousands of complete aircraft (freeware and payware repaints), regional and worldwide scenery packs, AI traffic, weather engines, utilities, sound packs, and missions. Most files are zip archives you drop into your FSX install folder. Some need to be placed inside SimObjects, others in Scenery, others in Effects — the file readme tells you which. If you're new to FSX modding, the README is your friend.
