Building a new Win 3.1 app in 2019
Yeo Kheng Meng published an article about building a Slack client for the very ancient 16-bit Windows 3.1 (released in 1993) in 2019. It is very interesting to read about the challenges of developing for such an old system. To solve problems, one has to dig in books instead of doing a Google search or asking on Stack Overflow.
It was a fun project, but I imagine there are still systems running in production using software as old as Windows 3.1 and developers who need to do support for those systems.