Date: 12/11/2012 
Why: Better usability

How many of you still have a Yahoo! email address? Now, when's the last time you actually used it? Exactly. To bring the hordes of people who once signed up for the email service back home, Marissa Mayer decided to redesign the entire system to make it seem as if it belonged in 2013. This meant cleaner visuals and better navigation. Yahoo Mail general manager Vivek Sharma was quoted as saying Mayer was actively involved in the process of redesigning the service and that it was one of her first initiatives. Under Mayer, the company also released an iOS app for Mail.