However, as a corporate sponsored project with multiple full time employees working on the documentation, it most likely fails your criteria in spirit.
ssl(3): [STILL INCOMPLETE] Manual page documenting the OpenSSL SSL/TLS library.
Any help is appreciated
In particular, use cases that demonstrate its value proposition are lacking, API docs miss examples, and the manual has some outdated parts. The layout of the site is a bit dated too, but "it worked for us".
It's like OpenCV but much better written. The only trouble is there's almost no documentation or tutorials for beginners.
Great project, no documentation whatsoever..