Web CTF Cheatsheet
https://github.com/w181496/Web-CTF-Cheatsheet
Awesome CTF Cheatsheet
https://github.com/uppusaikiran/awesome-ctf-cheatsheet
Introduction - CTF Field Guide
https://trailofbits.github.io/ctf/
overthewire.org
underthewire.org
tryhackme.com
ctf.hacker101.com/
picoctf.com
hackthissite.org
crackmes.one
hackthebox.eu