TestSubject - Test how your email subject line displays on mobile devices.
DeepMail - Diligently sourced emails. Accurate emails for Startups and established companies
analyze.email - Test the spam-y-ness of your emails
Rename Email - Easily change the subject of any email, by cloudHQ
Inbox Flows - Research and compare emails from top brands & competitors
ShowSubjectGmail - Edit the "subject" field when replying in Gmail!