The majority of computer users are familiar with the Windows graphical user interface (GUI). Most people know how buttons, toolbars, and tabs work, based on their experience with Microsoft Word or their email client. But contrast the consistent interfaces of client applications with online applications, and you find nearly every site does it differently. A user needs to learn how to use each Web application from scratch. While many applications aren't particularly complicated, it can still be a frustrating experience for a user to always feel like a newbie, needing to relearn an app interface again and again.