The login page, with buttons simplified into singular colors. The gray buttons are neutral actions, whereas Login is blue to signify progress.
The Library, modified to show more content (Friends, Achievements, Workshop, etc.) at once, as well as to streamline "favoriting" and filtering your game library down to more easily find what you want to play. The most significant addition to the client is the Friends sidebar. Previously relegated to a separate window, Friends is given a more prominent sidebar for easily accessing the client's most important feature, second only to games.
The Steam Overlay, already a facet of the Steam client, sets it apart from comparable storefronts. The Overlay appears on top of a game when pressing Shift and Tab simultaneously, allowing you to talk with friends, surf the web, and view other relevant game information without leaving your game.
The Overlay has been given the Library's "card"-like design for game information, as well as the Friends sidebar. This mockup also adds new "Downloads" and "Trading Cards" containers, which had only previously been manageable from the client itself.