RightInbox Adds Reminders to Gmail and Notifies You When Email You Sent Is Read

Firefox/Chrome: RightInbox is an awesome tool for boosting Gmail's capabilities. The extension when it first launched was designed to schedule email for sending later, but RightInbox since then has added even more useful features: email tracking, link click tracking, and email reminders.
Once you connect the add-on to your Gmail account, you'll find new buttons in Gmail for scheduling an email to be sent later, tracking an email you compose, and adding reminders to an email.

Install Mountain Lion on As Many Macs As You Want Without Purchasing Additional Copies

One of the upsides of OS X Mountain Lion's already low purchase price of $20 is that one copy can be re-downloaded and installed on any other Macs that you own for free. The downside, of course, is that if another Mac in the household doesn't share the same Apple ID as you, the buyer, you have to get another copy. As it turns out, there's a very simple solution so you can just reinstall from the same copy as many times as you need to.