It’s nice to have the ability to draw on attachments in Mail, but in actuality, it’s not so easy to make neat lines using a trackpad. So, rather than letting you send scribbles that look like they were done by a four-year-old, Markup will instantly recognize what you’re trying to draw, whether it’s a lopsided circle or crooked arrow. To use it, click the menu button that appears in the top-right of the attachment when you mouse over it. (MacLife)