Winteracter was always kind of a unique product, in that it allowed a pure Fortran solution for creating fairly complicated GUIs, packaged up as a nice product with pretty good technical support from the developers. But I always wondered about their business model and how many customers they had and how long it was going to last.
We used Winteracter for many years in my org, but ended up basically outgrowing it due to its limitations. I do have fond memories of using it though. The Windows version was fine but was really showing its age. The Mac version was not great, since it was X11/OpenMotif based, and the less said about that the better. I don’t think I ever used the Linux version (also X11/OpenMotif).
We ended up rewriting our GUI in Python and Qt/PySide, with the Fortran core as a shared library. This allowed us to have real and modern cross-platform support and a very sophisticated GUI that just was not possible with Winteracter. So we ended up with something that was not only free, but better in most or all ways.