Re: It wasn't just apps
Very much this. As Charles Petzold, the author of what was the "Bible" for Windows programming for much of the 90s once pointed out, there are examples from the Windows 1 SDK that can still be built and run on the most modern versions of Windows (nothing that requires e.g., file I/O as Windows 1.x still needed DOS APIs for that but window management, message processing, resources, etc. are all present and correct and largely unchanged). I don't think there is no any UI toolkit still in widespread use that could boast this.