I though about this and decided my favorite non-profit is public education.
To enrich someone's knowledge is a giving act. To open up oneself to the knowledge of another is heroic. It's easier to stay in a comfort zone in which one controls all the information coming and going, rather than to learn what is different from what one already understands to be true.
There was a time when public education was not mandatory. There could be a time when public education will no longer be available. Then it would be up to individuals to educate themselves, which could be evolutionary or could be isolationist.
Public education can be designed to open up the mind for a life-time of learning. Public education can teach essential skills needed in communities. Public education can be discourse and it can create the future.
Is public education a non-profit? I believe it is because the gain is not monetary but cognitive, soulful. There should be no selfish pride in public education; there should only be humility. Although public education has become an institution steered by politicos and line-towers, fact-checkers and disciplinarians, it should be owned by no one person or entity.
Public education is owned by the people for the people, and it should always be free.