Proprietary 'Proprietary systems' or products, limit you to the use of the offerings being created by the 'proprietor' or owner of the company. For example: only proprietary ink cartridges can be used on Epsom printers. Apple systems apps are proprietary - they can't be used on other systems Definition, Merriam-Webster Definition of proprietary (Entry 1 of 2) 1: one that possesses, owns, or ...
Proprietary to is the more popular construction. Currently, 'proprietary of' is almost unused according to Google Ngrams. Proprietary is an adjective. 'Proprietary to A' thus means 'proprietary with regards to A.' Replacing 'proprietary' with a more familiar adjective makes this easier to grasp: ' Big to me ' can be seen as meaning 'big, in my opinion,' and can be used to describe both ...
But there is certainly much that is proprietary - so even of many people know, they may not want to write about it at length here in stackexchange. Some people might find the use of "much that is" a bit stuffy, but I don't think it sounds very bad.
The OED provides: “crock pot n. Cookery (originally U.S.) (originally) = sense 1; (now) spec. (also with capital initials) (a proprietary name for) a lidded pot with an integral electrical heating element, for cooking food at low temperatures for long periods; a slow cooker.” They only have it as an open compound, crock pot, but you also come cross crock-pot and crockpot fairly frequently.
Software used and developed within an organization is often called either in-house or proprietary software, as opposed to shrink-wrapped of off-the-shelf software. Work done to develop software for a client is often called contract work, and is clearly distinguished from school assignments, side projects or pet projects.