Not only the manual, but Gnus itself. I remember this guy from the university (UiO) when he started working on Gnus. He was a small celebrity among us informatics students, and we all used Emacs and Gnus, of course.
Gnus was absolutely delightful back in the day. I moved on around the time I had to start writing non-plaintext emails for work reasons. It's also handy to be using the same general email apps and systems as 99.99% of the rest of the world. I still have a soft spot in my heart for it.
PS: Also, I have no idea whatsoever why someone would downvote you for that. Weird.