I’ve actually taken a bit of time to fix up, make user friendly, and publish a tool that I wrote a little while ago, and has been very useful to me.
The regular expressions tester engine basically provides a front-end to the Microsoft .NET Framework Regular Expressions engine, allowing you to test regular expressions you’ve written to your hearts content.
As usual, I’m releasing it as-is under the MIT licence, and as usual the source can be found on GitHub.
For a page which might have more information on it at some distant point in the future, but more importantly has a download and bugtracker link, see this page on my main website.