KNOPPIX is a bootable CD with a collection of GNU/Linux software, automatic hardware detection, and support for many graphics cards, sound cards, SCSI devices, and other peripherals. It can be used as a Linux demo, educational CD, rescue system, etc. It is not necessary to install anything on a hard disk due to on-the-fly decompression.
Sawfish (the window manager formerly known as Sawmill) is an extensible window manager using a Lisp-based extension language. All window decorations are configurable and all user-interface policy is controlled through the language. Its aim is to manage windows in the most flexible and attractive manner possible. As such it does not implement desktop backgrounds, application docks, or other things that may be achieved through separate applications. Sawfish is mostly GNOME-compliant; almost all configuration may be made through a graphical interface.
Window Maker is an X11 window manager designed to give additional integration support to the GNUstep Desktop Environment. In every way possible, it reproduces the elegant look and feel of the NeXTSTEP[tm] GUI. It is fast, feature rich, easy to configure, and easy to use. In addition, Window Maker works with GNOME and KDE, making it one of the most useful and universal window managers available.
spectrwm is a minimalistic tiling window manager that tries to stay out of the way so that valuable screen real estate can be used for much more important stuff. It has sane defaults and does not require one to learn a language to do any configuration. It was written by hackers for hackers and it strives to be small, compact, and fast.
FVWM-Crystal aims to create an easy to use, pretty, but also powerful desktop environment for Linux or other Unix-like operating systems. It uses the following programs: FVWM as a window manager and "main core"; different ways to provide icons on the desktop including support for many file managers and custom commands; xterm, aterm, mrxvt, or urxvt as terminal emulators; MPD or XMMS2 as music players (there's built-in support for controlling these programs), and several other tools for different functions, like setting a wallpaper or taking screenshots.
Enlightenment is a themeable, fast, flexible, and powerful window manager that is designed to be as configurable as possible in both look and feel. In addition, Enlightenment provides an applet API that provides functionality somewhere between the GNOME applet system and Dock Apps from Afterstep/WindowMaker. The current design aim is for Enlightenment to become a desktop shell.
AfterStep is a Window Manager for X which started by emulating the NeXTSTEP look and feel, but which has been significantly altered according to the requests of various users. Many adepts will tell you that NeXTSTEP is not only the most visually pleasant interface, but also one of the most functional and intuitive out there. AfterStep aims to incorporate the advantages of the NeXTSTEP interface, and add additional useful features.