RegexBuddy - RegexBuddy is your perfect companion for working with regular expressions.
Regex Forge - An Ultimate Regex Editor for macOS
RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
regular expressions 101 - Extensive regex tester and debugger with highlighting for PHP, PCRE, Python and JavaScript.
i Hate Regex - regex cheatsheet for the haters
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.