In the US, my understanding is that there are some pretty big legal lockdowns on Reverse Engineering things, as a favor to the big copyright holders (to prevent ripping DVDs, etc).
In Europe and most of the rest of the world, my understanding is that the right to Reverse Engineer something is better protected.
Siemens has its soft controllers, so it isn't completely unfathomable that someone else would have made a soft controller that is intended to work the same. This feels like a REALLY specific use case to me (S7 on Beckhoff HW). I'm curious how much money the company is making, or if the product exists to fulfill a specific request from a large user? Or is the beckoff HW liked that much better by its users, but they still want an S7 interface for reasons?
The Wiki says that it supports a variety of versions of Windows, not just CE. I'd be curious to see what they are using for the realtime layer, if they have one. As others have said, by itself, Windows and realtime pretty much don't go together, but there are ways to make it work.