FollowUpThen: Free and Easy Email Reminder

Some people respond to emails on time and some don’t. If you’ve a friend or contact in the latter category it’s worth giving FollowUpThen a shot. You don’t need to sign up for an account to use the service, either: simply CC the email to the service, using the amount of time between now and the follow-up as the user name and “followupthen.com” as the domain.

http://www.followupthen.com/