In fact, pretty much ALL software is proprietary. The exception being software written in the US before they joined Berne.
The distinction should be "open" and "commercial" (and maybe not even that!). Proprietary simply means "owned by" - a shop is open (it wouldn't be much use without it) but has a proprietor. As a simple example of what I mean, glibc is proprietary to the FSF. The fact they have released it under a Free licence doesn't mean they don't own it. And actually, it's Microsoft we have to thank for this new distorted meaning of the word "proprietary"!!!