Title: Xah Lee
Link: http://xahlee.info/
Description: Nearly 4,000 mathematics and programming, tutorials and essays written by Xah Lee, the eminent Emacs user. There is also an offline version which you can buy and support his work http://ergoemacs.org/emacs/buy_xah_emacs_tutorial.html.
Topic: _Guides _Programming _Mathematics
Paid: If you want the offline version, then yes.
Link: http://xahlee.info/
Description: Nearly 4,000 mathematics and programming, tutorials and essays written by Xah Lee, the eminent Emacs user. There is also an offline version which you can buy and support his work http://ergoemacs.org/emacs/buy_xah_emacs_tutorial.html.
Topic: _Guides _Programming _Mathematics
Paid: If you want the offline version, then yes.