Intro to Linux Window Manager ＆ Desktop Environment (Gnome, KDE, Xfce, xmonad, …)

This page is a overview of Window Managers and Linux Desktop Environments, with instruction on how to install them.

X11 is linux's graphical user interface engine. Practically ALL Linux's GUI apps are based on it. It can be used by itself without Gnome, KDE, etc.
X Window Manager is a layer on top of X11. There are tens of Window Managers, each one looks different, and have different set of keyboard shortcuts, customibility. Examples of Window Managers are: {awesome, enlightenment, FVWM, Sawfish, Scwm, dwm, ratpoison, xmonad, …}.
Desktop Environment is a Window Manager plus a complete set of apps (web browser, folder viewer, image viewer, image editor, text editor, video/music player, …). The most popular Linux Desktops are {Gnome, KDE, Xfce, LXDE, Unity}.

The term Shell, or Linux GUI Shell, is sometimes used to refer to a core part of Desktop Environment.

Almost all linux GUI apps are written using either Gnome's libary the “GTK+ toolkit”, or KDE's library the “Qt framework”. For most linux GUI app, you have to check which lib it's from. For example, the apps in Ubuntu are mostly GTK+ based apps.

Unity is default from Ubuntu. There are actually 2 versions of Unity: {Unity 2D, Unity 3D}. Unity-2D is the default when you have a slow GPU. Their appearance are almost identical though. The term “Unity” usually refers to Unity 3D.
Gnome and KDE are popular, classic, mainstream desktop.
Xfce and LXDE are light-weight desktops. Good for old laptops. LXDE looks like Windows 95.
{Awesome, Ratpoison/StumpWM, xmonad, …} are popular tiling window managers. They leaves no gab between windows, and are designed to be used primarily by keyboard (not mouse).

Just install it, then re-login. In the login panel, there's a menu to let you choose from installed desktops or Window Managers.

To install:

Xfce. sudo apt-get install xubuntu-desktop
LXDE. sudo apt-get install lxde
Xmonad. sudo apt-get install xmonad

similar for others. Do apt-cache search ‹name› to find the proper package name.

On RedHat/Fedora based linux, use YUM to install. yum is the command-line package-management utility for RPM-compatible Linux, similar to Debian-based linux's apt-get (Advanced Packaging Tool).

Example of using yum: sudo yum install xmonad-gnome.

(thanks to Jeff Weiss)

{Unity, KDE 4, Gnome 3} = Fancy

Unity and GNOME 3's UI are bleeding-edge, “simplified”, “smart”. Basically, they tried to innovate, and threw-away the classic desktop metaphor. The new UI is often more suitable to mom ＆ pop computer-illiterates, but annoying for those who know what they are doing. When Apple innovates UI, it usually works. But when linux folks try …

Linus switched to GNOME when KDE turned into fancy shit with KDE 4. Then GNOME 3 became fancy shit, so he switched to Xfce.

Old Machine? Use Light-weight Desktop: Xfce, LXDE

If you hate the fancy UI, or prefer a classic, standard UI that doesn't suck the blood out of your old GPU, then use Xfce or LXDE.

Xfce

LXDE

According to Wikipedia, LXDE beats Xfce in minimal memory consumption, while Xfce is similar to GNOME 2.

since GNOME moved to GNOME 3, leaving GNOME 2 dead in the water, some people forked GNOME 2 and is now named MATE (desktop environment).

Window Manager Only, Absolute Minimum Light Weight

Xfce and LXDE are light-weight, but they are still Desktops, with bundled GUI apps chosen for you. The following are bare minimum Window Managers. They are usable only if you know linux well.

Openbox

No desktop, no taskbar, no menu, no nothing. Once installed and in Openbox, the screen is complete blank except a text terminal. Right click on the blank screen to get a context menu. Use 【Alt+Tab ↹】 to see opened apps.

tried Openbox, decided it's unusuable, reboot back to xfce, but the wm is f�cked. Mouse/touchpad doesn't work anymore. Basic keys such as 【Alt+Tab ↹】 or 【Alt+Space】don't work. This means, i can't switch windows/apps, can't resize/move/hide windows, can't see a list of windows. The only thing you got that works is a small-window terminal. (lucky me!)