You're describing DDE. In use since Windows 2.0 and still functioning today in Windows 10, 32 years later.

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

https://docs.microsoft.com/en-us/windows/desktop/dataxchg/dy...

It's implemented with the WM_DDE_... series of messages. There's a library, DDEML, which wraps some of the complexities.