9wm - 9wm is an X window manager which attempts to emulate the Plan 9 window manager 8-1/2 as far as possible within the constraints imposed by X.
awesome - awesome is a highly configurable, next generation framework window manager for X. It is very fast, extensible and licensed under the GNU GPLv2 license.
Blackbox - Blackbox is the fast, lightweight window manager for the X Window System you have been looking for, without all those annoying library dependencies. Blackbox is built with C++ and contains completely original code (even though the graphics implementation is similar to that of WindowMaker).
Compiz - OpenGL compositing window manager. It has a plug-in system to be changed at runtime
dwm - dwm is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.
Enlightenment - Enlightenment is not just a window manager for Linux/X11 and others, but also a whole suite of libraries to help you create beautiful user interfaces with much less work than doing it the old fashioned way and fighting with traditional toolkits, not to mention a traditional window manager
Fluxbox - Fluxbox is a windowmanager for X that was based on the Blackbox 0.61.1 code. It is very light on resources and easy to handle but yet full of features to make an easy, and extremely fast, desktop experience. It is built using C++ and licensed under the MIT-License.
FVWM - FVWM is an extremely powerful ICCCM-compliant multiple virtual desktop window manager for the X Window system
i3 - i3 is a tiling window manager, completely written from scratch. The target platforms are GNU/Linux and BSD operating systems, our code is Free and Open Source Software (FOSS) under the BSD license. i3 is primarily targeted at advanced users and developers.
IceWM - IceWM is a window manager for the X Window System (freedesktop, XFree86). The goal of IceWM is speed, simplicity, and not getting in the user's way.
JWM - JWM is a light-weight window manager for the X11 Window System. JWM is written in C and uses only Xlib at a minimum. Because of its small footprint, JWM makes a good window manager for older computers and less powerful systems, such as the Raspberry Pi, though it is perfectly capable of running on modern systems.
Matchbox - Matchbox is an Open Source base environment for the X Window System running on non-desktop embedded platforms such as handhelds, set-top boxes, kiosks and anything else for which screen space, input mechanisms or system resources are limited.
Mutter - Mutter is a window manager for the X Window System, and is in the process of becoming a Wayland compositor; it became the default window manager in GNOME 3, replacing Metacity.
Openbox - Openbox is a highly configurable, next generation window manager with extensive standards support.
pekwm - pekwm is a window manager that once upon a time was based on the aewm++ window manager, but it has evolved enough that it no longer resembles aewm++ at all.
ratpoison - Ratpoison is a simple Window Manager with no fat library dependencies, no fancy graphics, no window decorations, and no rodent dependence. It is largely modelled after GNU Screen which has done wonders in the virtual terminal market.
Sawfish - Sawfish is an extensible window manager using a Lisp-based scripting language. Its policy is very minimal compared to most window managers. Its aim is simply to manage windows in the most flexible and attractive manner possible.
wmii - A small, scriptable window manager, with a 9P filesystem interface and an acme-like layout.
xmonad - xmonad is a dynamically tiling X11 window manager that is written and configured in Haskell. In a normal WM, you spend half your time aligning and searching for windows. xmonad makes work easier, by automating this.
X Desktop Environments
KDE - The KDE Software Compilation (KDE SC) is a desktop environment and an associated range of KDE Applications produced by KDE.
LXDE - The "Lightweight X11 Desktop Environment" is an extremely fast-performing and energy-saving desktop environment.
GNOME - GNOME is a desktop environment which is composed entirely of free and open-source software.
MATE - MATE is a desktop environment forked from the now-unmaintained code base of GNOME 2.
Xfce - Xfce is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly.
EDE - EDE is small desktop environment built to be responsive, light in resource usage and to have familiar look and feel.
Graphical Package Management Tools
Y PPA Manager - Search for packages in Launchpad PPAs.
PacmanXG - GUI front-end for pacman. Depends on neither GTK+ nor Qt, just X11.
pirut - pirut provides a set of graphical tools for managing software.
YaST - YaST is the main package management tool on openSUSE.
Partition Editor
GParted - GParted is a free partition editor for graphically managing your disk partitions.