Compiz - Compiz can be used as either a compositing manager to add fancy effects to your windows or as a full windows manager. Included effects include drop shadows, the desktop cube and expo view.
Console - For developers and others who like to work from the command line, Console adds capabilities that aren't available through cmd.exe. For example, it allows users to open multiple tabs, change the font and window style, use a text selection tool, and more.
DropIt - If your file system is a mess, DropIt gives you an easier way to clean it up than using the file copy-and-paste capabilities of Windows Explorer. With this app, you can create an icon on your desktop that sends files to the folder of your choice. Just drag your file to icon and it will move the file where you want it to go.
Electric Sheep - In his famous novel, Philip K. Dick wondered Do Androids Dream of Electric Sheep? This screensaver answers that question by connecting thousands of systems and using them to create ever-changing animations known as "sheep." And yes, the app now works on Android.
Emerge - This replacement for the Windows shell offers a minimalist interface based on applets. It lets users access programs via a right click instead of the Start Menu, and it offers an application launcher and virtual desktop capabilities.
Enlightenment - Compatible with both Gnome and KDE, Enlightenment is a fast, modular windows manager. The project also includes a large interface development library, some parts of which are usable on Windows, OS X and other OSes.
Florence - If you can't use your hands for some reason, or if you spilled Red Bull on your keyboard and are waiting for it to dry out, Florence can help you keep on typing. This app for the Gnome desktop puts a virtual keyboard on your screen that you can click with your mouse.
Fluxbox - Although it's not too flashy, this window manager is lightweight and fast. Key features include tabbing, editable menus, an application dock and more.
Icewm - Icewm's stated goals include "speed, simplicity, and not getting in the user's way." It currently supports 25 different languages.
Izulu - No window near your cubicle? This app automatically changes the background on your desktop to match current weather and time.
Kwin - The default window manager for the KDE Plasma desktop, KWin puts an emphasis on reliability and good looks. The latest version supports com-positing, that is, 3D window effects.
Launchy - If you hate to use the mouse, Launchy is for you. It lets you open applications, documents, folders, bookmarks and more with just a few keystrokes.
LCARS 24 - Looking for something fun to do with an old PC? This app adds Star Trek-like computer graphics to your screen, and it functions as an alarm clock and file manager, plus providing some other utilities. If nothing else, it makes for an interesting conversation piece.
LotseEscher - Fans of the artist M. C. Escher will enjoy this animated version of his Print Gallery drawing. If you like it, you may also like this developer's other screensavers: LotsaGlass, LotsaSnow and LotsaWater.
Matrixgl - For those who love the Matrix movies, this screensaver features falling green characters that create images of characters from the The Matrix Reloaded.
Metacity - The default window manager for Gnome 2.x, Metacity is designed to be as usable and unobtrusive as possible, and might be described as a little plain. The project owners themselves say, “Many window managers are like Marshmallow Froot Loops; Metacity is like Cheerios.”
Pnotes - Much like real-world sticky notes, PNotes lets you leave virtual sticky notes for yourself on your computer. Interesting features of this app include audio notes, scheduling, password protection, encryption, transparency and more.
Really Slick Screensavers - If you're looking for a screen-saver that's a little bit out of the ordinary, check out Really Slick. It includes a dozen different colorful (and sometimes nausea-inducing) screen-savers.
Sticker - Sticker is a Windows 7-compatible electronic post-it note app. Unlike some similar apps, it lets you put notes directly on the desktop as if they were icons.
Wikiquote Screensaver - If you prefer a screen-saver that's a little more philosophical, check out this app. You type in a topic and press save, and it will pull up random Wikiquotes on the topic.
VirtuaWin - Most Linux/Unix windows managers make it easy to switch between desktops, but to accomplish the same thing on Windows, you usually have to log out and log back in as another user. This app lets you save up to nine different desktops and switch between them quickly. It's helpful if you're multi-tasking and need one set of apps for one project and other set for a different project.
WindowsPager - WindowsPager offers very similar functionality as VirtuaWin, with a different interface for switching between work spaces.