Theoretical Physics Reference by Ondrej Certík

The only one on GitHub. In RST and renders to HTML with image formulas.

Too "direct formula overload" at first look.

By the creator of SymPy, who works at Los Alamos National Laboratory and has a PhD in chemical physics: swww.linkedin.com/in/ondřej-čertík-064b355b/ Man, big kudos to this dude.