I looked into using Dewey Decimal for a hobby project. OCLC has a de facto monopoly on it due to the Worldcat database. They're a non-profit, but they're supported by having libraries pay a subscription fee for Worldcat. Back when OCLC was founded, the idea that people would want to have a copy of a card catalog for personal use was laughable, so I'm sympathetic to the people that set up their funding model. It's far…
It came out when the Library Hotel in NYC used some of their notation as their room numbers and were sued. Everyone was WTF?