Regex Coach - interactive regular expressions is a Builder with a nice GUI

The Regex Coach - interactive regular expressions
Via lemonodor
I find a great graphical interactive tool for building perl compatible regular expressions.

The Regex Coach is a graphical application for GNU/Linux and Windows which can be used to experiment with (Perl-compatible) regular expressions interactively. It has the following features:

• It shows whether a regular expression matches a particular target string.
• It can also show which parts of the target string correspond to captured register groups or to arbitrary parts of the regular expression.
• It can "walk" through the target string one match at a time.
• It can simulate Perl's split and s/// (substitution) operators.
• It tries to describe the regular expression in plain English.
• It can show a graphical representation of the regular expression's parse tree.
• It can single-step through the matching process as performed by the regex engine.
• Everything happens in "real time", i.e. as soon as you make a change somewhere in the application all other parts are instantly updated.

Update:
See also ONLamp.com: Five Habits for Successful Regular Expressions [Aug. 21, 2003]