HTTP Archive : The HTTP Archive tracks how the Web is built.
Inj3ct0r 1337day.com : Exploit database separated by exploit type (local, remote, DoS, Poc, etc.)
mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
This article explains what secure headers are and how to implement these headers in Rails, Django, Express.js, Go, Nginx, and Apache.