RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.

Followup.cc - FollowUp for email is a lightweight productivity suite that keeps your conversations and tasks from slipping through the cracks. Set perfectly timed reminders that arrive at the top of your inbox, right when you need them.

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.

Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.

rubular - A ruby based regular expression editor

Boomerang for Outlook - Boomerang for Outlook offers email productivity tools to track, schedule and send mails at the right time.