Embed a Windows application within a 3D Unity game

Basically, I’d like to have my Unity game start up a separate windows application and show its output inside the game, say as a texture on a flat plane. I’d also like the game to be able to give input to the application, via interactions within the game. Is this possible? If it is, do I need to deign the embedded application myself, or could I embed any application?

Currently we support doing things the other way - embed Unity into other application. Perhaps you can do it that way?
Embedding other application into Unity is possible, but both application have to be designed with that in mind, there might be weird issues, in particular with input, as I’m not sure anyone has tried that before.