regexpviewer is a small app for
regular expression experimentation.

Move the mouse over the () matches and see the corresponding text.
Available from
http://dedasys.com/freesoftware/applications.html
(link broken 2012-11-11 - use
http://dedasys.com/freesoftware/files/regexpviewer.tgz
instead)
Similar to
Visual REGEXP.
EKB I like it! It's simple, with a clean and clear interface.