RegExr.com is an online tool to learn, build, and test Regular Expressions. It was created by Grant Skinner and the nice people at gskinner.com.
RegExr vs RegexBuddy opinions
Support only 2 engines while RegexBuddy 3.6 can simulate 15 flavors (Java, perl, python, ruby, tcl,...)
Much much less functionality.
easy to use, web-accessible, replace function, documentation, explanation function
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 or web designer with an extensive knowledge of regular expressions.
Expresso vs RegexBuddy opinions
iHateRegex offers an easy way for developers to find helpful and reusable regular expressions while also providing an intuitive playground to interact with regex snippets to create or just learn.
jRegExAnalyser is an interactive tool written in Java to write, test, debug, analyse and profile regular expressions. Its free and Open Source software, licensed under the terms of GPLv2 with Class Path Exception.
jRegExAnalyser vs RegexBuddy opinions
regex tester, but missing other engines' regex (Perl Python Tcl etc)