regex101 : Free PCRE-based regular expression debugger with real time explanation, error detection and highlighting.
When can I use... : Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers.
Gophercises : FREE coding exercises for budding gophers
XSS Filter Evasion Cheat Sheet - OWASP : This article is focused on providing application security testing professionals with a guide to assist in Cross Site Scripting testing.
TraceKit : Not all browsers support stack traces on error objects, but TraceKit squeezes out as much useful information as possible and normalizes it.
