Trick with transparent window

Source code I'm not uploaded, because you can find it at:

https://bobobobo.wordpress.com/2008/02/13/when-to-use-the-createwindowex-function-and-how-to-create-a-translucent-window-using-it/

I uploaded the .exe file for those who don't have time to compile.

On ReactOS:

On WinXP:

That this is not just a one-time initialization is proven by the fact that the clock hand moving can be seen through it, as a seconds number.

On Win10:

project.exe