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X primarily defines protocol and graphics primitives – it deliberately contains no specification for application user-interface design, such as button, menu, or window title-bar styles. Instead, application software – such as window managers, GUI widget toolkits and desktop environments, or application-specific graphical user interfaces – define and provide such details. As a result, there is no typical X interface and several different desktop environments have become popular among users.
A window manager controls the placement and appearance of application windows. This may result in desktop interfaces reminiscent of those of Microsoft Windows or of the Apple Macintosh (examples include GNOME 2, KDE, Xfce) or have radically different controls (such as a tiling window manager, like wmii or Ratpoison). Some interfaces such as Sugar or Chrome OS eschew the desktop metaphor altogether, simplifying their interfaces for specialized applications. Window managers range in sophistication and complexity from the bare-bones (e.g., twm, the basic window manager supplied with X, or evilwm, an extremely light window-manager) to the more comprehensive desktop environments such as Enlightenment and even to application-specific window-managers for vertical markets such as point-of-sale.
Many users use X with a desktop environment, which, aside from the window manager, includes various applications using a consistent user-interface. Popular desktop environments include GNOME, KDE Software Compilation and Xfce. The UNIX 98 standard environment is the Common Desktop Environment (CDE). The freedesktop.org initiative addresses interoperability between desktops and the components needed for a competitive X desktop.