X11

X11 is a computer software and network protocol that provides Graphical User Interphase(GUI) for users. It is a standard on Unix, Linux and other Unix-like operating system, and many other operating systems. X11 provides basic functions for a GUI: drawing, moving windows, interacting with mouse cursor, it doesn't provide features of a user interface buttons, menus, title bar of window, these features are provided by softwares such as window managers, GUI widgets toolkit.

X originated at MIT in 1984. The current protocol version, X11, appeared in September 1987. The X.Org Foundation leads the X project, with the current reference implementation, X.Org Server, available as free and open source software under the MIT License and similar permissive licenses.