Regular-Expressions.info provides an in-depth resource featuring a comprehensive regex tutorial, examples, reference, and tools for learning and mastering regular expressions.

RegExLib is a searchable library and testing tool for regular expressions, used by developers needing pattern matching solutions across various programming languages.

RexEgg provides a comprehensive, advanced tutorial and reference for Regular Expressions (regex), covering syntax, tools, and application across multiple programming languages.

Debuggex is an online visual regex tester tool supporting JavaScript, Python, and PCRE, allowing users to test and visualize regular expressions live.

Regex Tester is an online tool to learn, build, and test Regular Expressions (RegEx) for Javascript and PCRE with real-time results.

Emailregex.com provides near-perfect, copy-paste email regular expressions (RFC 5322 compliant) for developers in various programming languages.