It looks as though Google is testing out a brand new design for its popular web based Gmail service, based on information from Geek.com. The redesign appears as though it will bring the Google web email app more in-line with its upcoming mobile counterpart, both in terms of aesthetics and functionality.
With its email service, Google usually introduces new features and UI elements slowly and in ways that aren't overly disruptive for avid Gmail users, but the recent images in question show quite a different interface entirely. We see a much more simplified layout with a responsive design and a wider main panel for recent emails. It is very similar to the leaked images spotted last month of the new Gmail for Android design.
The new design does away with the left and/or right fixed side panels, replacing them with Google+ style collapsible menus, allowing for a number of convenient viewing options. On the left, you'll find all the usuals including your various email folders and groups, and on the right there is a Hangouts option to launch chats, a compose email button, and an interesting reminders option that allows users to store unfinished emails or notes and other things in one place.
We also get to see the pin system from the mobile Gmail redesign leaks in place here, which essentially replaces the "star" system we have now and allows for custom organizing and viewing options of important messages.
The right hand button style, fly-in menus, "Upcoming" section, and new pin system are all features we saw inside last month's mobile Gmail redesign. There is no official word that any of these features will actually make it into Gmail the way we are seeing them now, but it wouldn't be out of the question to see something more come out of Google I/O in June, or even sooner.