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.
SQL Injection Cheat Sheet : Samples are provided to allow reader to get basic idea of a potential SQL Injection attack and almost every section includes a brief information about...
HTTP API design : This guide describes a set of HTTP+JSON API design practices, originally extracted from work on the Heroku Platform API.
CSSdoc : This is a draft to bring automatic documentation to CSS files, like its known for JavaScript and PHP files through JavaDoc/DocTags.