It doesn’t need to be non-proprietary, it only has to support fairly well standard protocols and open standards.
The BubbleUPnP app is a good example in this respect. It can control devices that implement OpenHome, Chromecast and UPnP/DLNA standards. It is very stable and very well supported.
Other examples of software artifacts that I very much like are MinimServer, MPD and upmpdcli. They work flawlessly and are very well supported.
Examples of software that I very much dislike are the system running on the Naim Core, in particular its UPnP server. Generally speaking, I have found manufacturer-specific software solutions for Hi-Fi devices quite disappointing, in comparison with the products mentioned above. I haven’t tried any dCS software so far.