regexxer - regexxer is a nifty GUI search/replace tool featuring Perl-style regular expressions.
RegexBuddy - RegexBuddy is your perfect companion for working with regular expressions.
PowerGREP - Quickly search through large numbers of files on your PC or network using powerful text patterns to find exactly the information you want. Search and replace with plain text or regular expressions to maintain web sites, source code, reports, ...
Regex Forge - An Ultimate Regex Editor for macOS
dnGREP - dnGrep allows you to search across files with easy-to-read results.
Patterns - Patterns is a simple yet powerful tool for working with regular expressions.