Leaked screenshots show a new user friendly interface for Gmail on the desktop browser that would redesign your inbox in totally different Interface. Google has habit to test new features for its various products but on the same time, it typically changes Gmail slowly. Google Hangouts is integrated into the new Gmail interface, now you just need to click on the chat-bubble-like icon at the bottom right corner of the display in order to pop out a sidebar that allows you to chit-chat with your friends and make video calls.
Source: https://thehackernews.com/2014/05/leaked-screenshots-suggest-new-gmail.html