一、X window manager
An X window manager is a window manager which runs on top of the X Window System, a windowing system mainly used on Unix-like systems.
gnome 1:Sawfish window manager
gnome 2:Metacity window manager
gnome 3:Mutter window manager
二、gnome-shell and gnome-panel
gnome-shell : the core user interface of the GNOME desktop environment starting with version 3
gnome-panel : a highly configurable launcher and taskbar for GNOME;
been replaced in GNOME 3.x by default with GNOME Shell;
serves as Fallback Mode when Mutter can not be executed, although it can still be activated if a user still wishes to use it as their default desktop.
三、Fallback Mode
GNOME 3 also features a more traditional GNOME Panel interface available as a "Fallback Mode" in situations where the GNOME Shell cannot launch due to a computer not meeting its higher hardware demands such as compositing and further desktop effects, although
it can also be toggled to be activated by the user.
The Fallback mode has most of the same features as the old GNOME Panel, including the placement of a limited number of applets and the ability to move them around panels, although the mechanism for doing this has been slightly altered (the user must press
the ALT key).
Both the GNOME Shell and the Fallback mode can also be further customized through the use of the "Gnome Tweak Tool", allowing users to regain a traditional desktop, change themes and fonts, and change various settings that are normally unavailable.
Fallback mode was removed in GNOME 3.8 and replaced with a suite of officially supported GNOME extensions named 'GNOME Classic'.
四、MATE
GNOME 3 replaced the classic desktop metaphor with a new interface built on top of GNOME Shell.
It led to some criticism from the Linux community. Many users refused to accept the new GNOME and called for someone to continue development of GNOME 2.
The MATE project was started by an Arch Linux user in order to fulfill this task.
It intends to maintain the GNOME 2 codebase and application suite, keeping them up to date while also offering a traditional GNOME 2 experience.
五、cinnamon
Cinnamon is a user interface. It is a fork of GNOME Shell, initially developed by (and for) Linux Mint.
It attempts to provide a more traditional user environment based on the desktop metaphor, like GNOME 2.
Cinnamon uses Muffin, a fork of the GNOME 3 window manager Mutter, as its window manager from Cinnamon 1.2 onwards.
It was released with Linux Mint 12 "Lisa" in November 2011, but fell short of expectations.Thus in January 2012 the developers of MGSE announced the Cinnamon shell, a fork of the GNOME Shell.
It was intended to maintain the underlying technology of GNOME Shell, including Mutter and GTK+ 3, while providing a more traditional, GNOME 2-like user interface.
参考：维基百科