https://www.w3schools.com/html/default.asp
https://developer.mozilla.org/en-US/docs/Web/HTML
https://html.spec.whatwg.org/
http://html.com
http://sololearn.com
http://codepen.io
https://www.w3schools.com/html/html_exercises.asp
https://www.practiceboard.com/
https://www.codecademy.com/learn/learn-html
https://code.visualstudio.com/
https://atom.io/
https://www.sublimetext.com/
https://notepad-plus-plus.org/
http://lighttable.com/
