The X-Windows environment is similar in many ways to other windowing sytems such as Microsoft Windows (95/98/2000/NT) and Mac OS. It provides a graphical interface for applications such as web browsers, drawing and graphing programs, file managers, word processors, spreadsheets, and many others. There are numerous window managers that can be used. Some emphasize more point-and-click techniques while others rely more on shell commands (see Section I.3 for some of these commands). [Aside: the Unix shell is just a program that acts as a buffer between you and the operating system. Its role is as a command interpreter. It is similar to the MS-DOS and VMS environments if you happen to be familiar with them.] Four of the most common X-Windows environments are listed here with a brief description of each.