Burp Suite

HTTPLeaks

Many different ways to leak data from html

https://github.com/cure53/HTTPLeaks

Page with general CTF/PenTesting guides, tips and tricks

https://book.hacktricks.xyz/

Awesome list with pentest links, tips, cheatsheets

https://github.com/coreb1t/awesome-pentest-cheat-sheets

PortSwigger Web Security Labs - A MUST for web penetration testing!

All labs | Web Security Academy

infoslack/awesome-web-hacking

University Courses:

Stanford - CS 253 Web Security

https://web.stanford.edu/class/cs253/