The Regex Coach
The Regex Coach was developed at a time when I didn't have this NBS naming thing I have now.
There is a Application for Windows with the same name but I wanted something that works on MacOsX and Linux aswell, Java makes it possible.
Developing regular expressions should be much easier with this tool. You can test your expressions directly on a string, matches will be displayed red below. You can also activate different options (like case-sensitivity). There is also the possibility of replacing the found string with an other string and you normally have a punch of options.
The Application can be downloaded hier.