The Open Web Application Security Project (OWASP) is a community, founded in 2001, which produces and makes available for free articles, methodologies, tools...
Every year, it publishes the Top 10 Web security vulnerabilities. It publishes the OWASP Testing Guide: a guide to best practices in depentesting.
It publishes the OWASP Development Guide: a guide to writing code without security holes. Official website: https://www.owasp.org