Tech Stack Fingerprinting

The CVE database (https://cve.mitre.org/cve/search_cve_list.html) contains publicly disclosed vulnerabilities. You can use its website to search for vulnerabilities that might affect your target.
Wappalyzer (https://www.wappalyzer.com/) identifies content management systems, frameworks, and programming languages used on a site, BuiltWith (https:/builtwith.com/) is a website that shows you which web technologies a website is built with.
StackShare (https://stackshare.io/) is an online platform that allows developers to share the tech they use. You can use it to collect information libraries and Node.js packages.
Retire.js (https://retirejs.github.io/retire.js/) detects outdated JavaScript about your target.