Engelbart is generally credited as the inventor of windows with his pioneering studies on the NLS system during the mid-1960s . Teitelman  argues that Smalltalk [46, 47] is the first graphical windowing system that used movable overlapping windows. It is also the first system to use cut-and-paste to transfer text among multiple windows.
The DLisp  system is the first system to support multiple fonts in windows. Various schemes are proposed to handle display complexity such as windows going grey and fading away if not touched for a long period of time, and arranging related windows into desktops.
Interlisp-D  is an object-oriented successor of Smalltalk. There is a standard set of objects that can be displayed and users can add their own objects as well.
Tajo  is among the first systems to use icons. Icons are small labeled images representing the closed state of windows. It also provides a solution to the display complexity problem. Tajo also introduced scrollbars, sub-windows, popup and static menus.
Viewers (Cedar)  is the first graphical windowing system that uses tiling . In tiled strategies, windows are not allowed to overlap. Some of the tiling systems, allowed transient windows to overlap. Xerox Star  also uses a tiling strategy, with up-to 6 windows. Tiled windows can be organized either in columns as in Cedar , or arbitrarily as in RTL . The first version of Microsoft Windows  also uses tiling.
Apple Lisa  and later Apple Macintosh  made their overlapping windowing system very popular which was followed by later versions of Microsoft windows.
Rooms [57, 58] introduced multiple virtual screens, where windows can be organized into each screen. Henderson and Card call these virtual screens workspaces, where each task is devoted a workspace. An overview of workspace layouts is also provided. Users can switch to other tasks either using the overview or the doors between workspaces for rapid transitions. This approach has been taken by other systems as well, such as the X window manager vtwm. These system are generally referred to as multiple-screen multiple window systems.
The innovations provided by these pioneer windowing systems were quickly followed by many other systems. SunWindows , NeXT Step, OPEN LOOK , OSF/Motif, and Sun NeWS  are other important window managers that had wider usage than the above pioneering systems. Recent research work on tiled windowing interfaces include the Plan9  where text windows are organized in columns.