RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
Boomerang Respondable - Write perfect emails with Artificial Intelligence
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.
Wordzen - We write your emails for you. Literally.
rubular - A ruby based regular expression editor
Mailbutler - Mailbutler adds lacking functionality to email clients and increases your productivity