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I think they generated it using Sphinx, which I heartily recommend as a tool -- you write your docs in REST, and it generates HTML (with built-in JavaScript search), PDF or other formats. It was developed for the latest version of the Python docs.

http://sphinx.pocoo.org/

Another vote for Flask. The Sintra docs are also quite good. http://www.sinatrarb.com/documentation

Related to Sinatra, the Padrino docs and guides are really good. On top of reference style documentation, guides and tutorials like the ones at http://guides.rubyonrails.org/ that are topic based are really helpful

Thought I'd get to Flask before Steve, but clearly I was mistaken. Another vote for Flask. Gorgeous.

Also: Flask's documentation is so gorgeous it almost convinced me I needed to use the framework even though I knew didn't need to use it.