Regular Expression Workbench (v2 by Eric Gunnerson)
Regular Expression Workbench is a small tool that allows you to experiment with and test .NET regular expressions. While some "cheat" sheets exist ( see RegexLib.com or Regegg.com ) and some great books (e.g., Mastering Regular Expressions the expressions can quickly become complex and its not always apparent that they work (or why they don't work). This tool is a handy "open source" tool that can be used to explore and iteratively develop regular expressions.
Eric Gunnerson had posted the announcement of the v2.0 code on his blog, which linked to gotdotnet. Unfortunately that site is now defunct and the source code is now unreachable. However, I had taken a snapshot of the code back in 2006 and contacted Eric for his permission to publish it here on github (or to see if he had already done so).
#Details Please see short descriptive file for more details
#Alternatives Expresso and Regulator - see Regulator Code have been around for a long time, however Expresso is closed-source and back when I grabbed the Regular Expression Workbench code I think Regulator was not fully open sourced.