DevDocs

DevDocs – “DevDocs is a fast, offline API documentation browser with 100+ docs including HTML, CSS, JavaScript, PHP, Ruby, Python, Go, C, C++, jQuery, and more. DevDocs combines multiple API documentations in a fast, organized, and searchable interface.”

I think that this is one of the best sites for documentation.  They cover practically everything.  This is a site that I use regularly and is a favorite of mine.