I have been doing a lot of regular expression parsing at work. Writing regular expressions are hard, and testing it is even harder. Regexpal and Debuggex are some of the popular web based Regular expression testing tools available. Inspired by the idea behind these tools, I wrote a simple cross-platform regular expression tester, RegexMate in PyQt. Initial version of RegexMate can highlight matches, groups and supports some regex flags as well.
I'm planning to add syntax highlighting for the regex pattern and additional options like replace and split in the upcoming releases. Stay tuned.