I always liked Cisco documentation, besides the documentation for each product in great detail, as it was in the 80's, everything in PDF, you also have links to

I always liked Cisco documentation, besides the documentation for each product in great detail, as it was in the 80's, everything in PDF, you also have links to manuals of a bunch of technology that the product support, just not the product. Well structure and organized. I miss that in many products and software nowadays.