regex101 : Free PCRE-based regular expression debugger with real time explanation, error detection and highlighting.
WebPlatform.org : Web Platform Docs is a community-driven site that aims to become a comprehensive and authoritative source for web developer documentation.
Inj3ct0r 1337day.com : Exploit database separated by exploit type (local, remote, DoS, Poc, etc.)
HTML5 Please : Look up HTML5, CSS3, etc features, know if they are ready for use, and if so find out how you should use them – with polyfills, fallbacks or as they
