I like the postgres docs as much as anyone but those flow diagrams sqlite has for commands are incredible and I wish pg had something like them. I know postgres tends to have way more options and they'd be unwieldy in some cases but still valuable I think.
Yeah those are nice. sqlite also has great internal design docs too, on par with the kernel. Surprised it slipped my mind actually as it's one of the best maintained and documented projects full stop.
The Linux kernel however is by far my favourite because of the in-depth design documents in-tree in easy to read plain-text format.