Valve It's a mockup of something that's being worked on that doesn't have a date.

Article taken from GamingOnLinux.com.

Recently, some images 'leaked' in a Steam update that showed off a shiny new look for the Steam client and Valve have confirmed it is being worked on. Thanks to SteamDB for noticing and putting the images up.See the interview below (skip to 30 minutes):You can see one of the images that leaked below:What they said:The Steam client is in need of an overhaul, as it's old and lacking in so many areas. Hopefully we will see something come of this, as I actually really like that design.