Right Inbox - Schedule Emails in Gmail To Be Sent Later
Gestimer - For those little reminders during the day
Recurrr - Send recurring emails
Timer Tab - Online countdown timer, alarm clock, and stopwatch.
FollowUpThen - The simplest way to schedule an email reminder
Online Stopwatch - Online Stopwatch is free to use online tool that allows you to keep track of the important events and tasks that you are performing.