HTML
one-html-page-challenge
The goal is to create anything you want within 1 single html file. Practice your skills with no assistance from libraries, no separation of files, and no assistance of a modern framework. How creative can you be with such restrictions?
JavaScript
2ality – JavaScript and more
To learn JavaScript in depth, make you proficient in JavaScript.
Regexper
Transform your regexper to clear graph.
CSS
Griddy
Learn the CSS Grid!