RegexPal Now Open Source
RegexPal (easily the most del.icio.used regex tester 
) is now released under the Creative Commons Attribution-Share Alike 3.0 License GNU LGPL.
There are certainly many more features that can be added to the app and things that can be improved, so if you are interested in helping out or creating your own version, you are welcome to do so. If there is interest I'll create a Google Code project, but for now there is a package you can download which includes all files for the regexpal.com website. Two of the files in the package (xregexp.js and helpers.js) are dual-licensed under the MIT License.
If you're only interested in the JavaScript, you can see the three source files here:
For regex aficionados particularly, there is some stuff here you might find interesting, including the latest, as-yet-unreleased version of my XRegExp library, and the regex syntax parser used for RegexPal's syntax highlighting (which includes lots of details on the minutiae of regex syntax and cross-browser regex handling).
Comment by Sebastian Werner on 11 November 2007:
Wow thanks. Yes a google code project would definitely be helpful.
Comment by Steve on 11 November 2007:
Aight, if one more person asks for it, I’ll set up the project.
Comment by Arnab on 17 December 2007:
Thanks for your great effort! ya I would love to see this in google code project
Comment by Steve on 17 December 2007:
Okay, gimme a few days and I should have a project set up somewhere. Not sure if it will be at Google Code, because due to their strong anti-license-proliferation stance they only allow projects hosted there to use one of a small number of licenses – which does not include the Creative Commons Attribution–Share Alike license RegexPal was released under. So, I’ll either up the version number and release it under a different license or host it elsewhere.
Comment by Steve on 22 December 2007:
Okay, it’s set up here: http://code.google.com/p/regexpal/
Version 0.1.4 is licensed under the LGPL. RegexPal needs tons of work… if anyone wants to get involved in its development, please leave a comment here or email me at: steves_list at hotmail dot com.
Comment by Justin on 9 January 2008:
What features are you looking to add?
Comment by Steve on 9 January 2008:
@Justin, see http://code.google.com/p/regexpal/issues/list for starters. Some of the bigger features I think would be cool are a real-time regex explanation tree, more consistent cross-browser rich-text fields (for syntax and match highlighting), match and subgroup listings, the ability to replace matches with other text (using a syntax highlighted replacement field), JavaScript code generation, etc. But there are many other big and small things that could be useful too. Longer term, I want to be able to do automatic regex generation.
Comment by Oliver Steele on 21 April 2008:
This looks great!
I wrote a tool for this a few years ago http://osteele.com/tools/rework/ , that has some features that I like: code generation for JavaScript/PHP/Python/Ruby; display a parse tree of the regex; display the FSA (currently busted?); display a list of matches. If I get some free time I’ll look at adding some of that functionality to your project, but in the meantime feel free to mine it for ideas and/or code — there’s no download page but the sources are unmimized. I hereby license it under the MIT License and the LGPL.
Comment by Steve on 21 April 2008:
@Oliver Steele, very cool! I’m a big fan of reWork, not to mention reAnimator and a lot of your other stuff. RegexPal’s Quick Reference is lightly adapted from reWork’s Help tab (noted here, and now also on the version history page).
I just did an svn commit to bring things on Google Code up to date with regexpal.com (minor changes only). I’d love to add some of your reWork features to RegexPal. Unfortunately, I probably won’t be able to look into it myself in the short term due to a bunch of things going on right now.