Win32 was an early widget set for Windows, Microsoft created a new one every few years until 2012, when it came out with the unwanted Metro. Since then it's been unclear what widget set Microsoft wants users to use, "use Electron" seems to be as official any answer.

In the case of Linux there are an even larger number of widget sets: see

https://en.wikipedia.org/wiki/List_of_widget_toolkits