MGR (ManaGeR) is a graphical window system. The MGR server provides a builtin window manager and windowed graphics terminal emulation on color and monochrome bitmap displays. MGR is controlled by mousing pop-up menus, by keyboard interaction, and by escape sequences written on pseudo-terminals by client software.
MGR provides each client window with: termcap-style terminal control functions, graphics primitives such as line and circle drawing; facilities for manipulating bitmaps, fonts, icons, and pop-up menus; commands to reshape and position windows; and a message passing facility enabling client programs to rendezvous and exchange messages. Client programs may ask to be informed when a change in the window system occurs, such as a reshaped window, a pushed mouse button, or a message sent from another client program. These changes are called events. MGR notifies a client program of an event by sending it an ASCII character string in a format specified by the client program. Existing applications can be integrated into the windowing environment without modification by having MGR imitate keystrokes in response to user defined menu selections or other events.
MGR currently runs on Linux, FreeBSD, Sun 3/4 workstations with SunOS, and Coherent. Various older versions of MGR run on the Macintosh, Atari ST MiNT, Xenix, 386-Minix, DEC 3100, and the 3b1 Unix-pc. Many small, industrial, real-time systems under OS9 or Lynx in Europe use (another variant of) Mgr for their user interface. The programming interface is implemented in C and in ELisp, although supporting clients written in other languages is quite easy.
Running MGR requires much less in resources than X, or even gcc. It does not have the user-base, software repertory, or high-level libraries of X or MS-Windows, say, but it is quite elegant and approachable.
It has been said that MGR is to X as Unix was to Multics.
MGR consists of a server with builtin window manager and terminal emulator, and clients which run in this terminal emulator and use it to communicate with the server. No resource multiplexing is done.
X11 consists of a server and clients, which usually connect to the server using a socket. All user visible things like terminal emulators, window managers etc are done using clients. No resource multiplexing is done.
8.5, the Plan 9 window system, is a resource multiplexer, as each process running in a window can access /dev/bitblt, /dev/mouse and /dev/kbd in its own namespace. These are multiplexed to the /dev/bitblit, /dev/mouse and /dev/kbd in the namespace of 8.5. This approach allows one to run 8.5 in an 8.5 window, a very clean design. 8.5 further has an integrated window manager and terminal emulator.