Rapportive is the ultimate email informant that plugs directly into Gmail . It shows you everything about your contacts right in your inbox. In other words, it's a Rolodex on steroids.

If knowledge is power, Rapportive, owned by LinkedIn, is The Incredible Hulk. The app automatically populates a column on the right hand side of your inbox with the everything you could ever want to know about the person you are emailing. Their photo, job title, location, social media feeds and connections you have in common.

For example, you could be emailing a potential new client and see that they just tweeted about a great new restaurant in town they're hoping to check out. Boom. You know EXACTLY where you're going to take them to celebrate the closing of your deal.