ReactOS is a rather interesting open-source project that is considered by many to be a direct and free drop-in replacement for Windows, especially if you don’t want to be locked in to Microsoft’s proprietary ecosystem. One of its goals is to allow customers to run Windows apps and drivers in an open-source environment (reminiscent of Windows XP) that they can trust, and it has made many advancements in this regard. It supports Microsoft’s FAT file system, Registry caching, native .zip handling, and is even capable of running Microsoft’s iconic Hover! in fullscreen. Now, the project is celebrating its 30th anniversary.
Depending on the situation there may be even older hardware/windows in use.
At my last job there was a windows 2000 computer still in use until like 2 years ago. None of the motherboard connections were still being made anymore. None of the drivers for the specialized devices existed for anything newer. The computer was air gapped and a replacement machine was commissioned, but it was still there doing its thing until the HDD failed.