Screenlets!

Rainmeter is a desktop customization platform. Through Rainmeter, you can enhance your Windows computer at home or work with skins: handy, compact applets which float freely on your desktop, much like Windows Sidebar gagdgets, or dashboard widgets for the Mac. Rainmeter skins provide you with useful information at a glance. Its easy to keep an eye on your system resources, like memory and battery power, or your online data streams, including email, RSS feeds, and weather forecasts. Many skins are even functional: they can record your notes and to-do lists, launch your favorite applications, and send your tweets to Twitter - all in a clean, unobtrusive interface that you can rearrange and customize to your liking. »

Conky is a free, light-weight system monitor for X, that displays any kind of information on your desktop. Originally a fork of Torsmo, Conkys torsmo-based code is BSD licensed. New code in Conky has been licensed under the GPL 3.0.

How many times have you walked up to a system in your office and needed to click through several diagnostic windows to remind yourself of important aspects of its configuration, such as its name, IP address, or operating system version If you manage multiple computers you probably need BGInfo. It automatically displays relevant information about a Windows computer on the desktops background, such as the computer name, IP address, service pack version, and more. You can edit any field as well as the font and background colors, and can place it in your startup folder so that it runs every boot, or even configure it to display as the background for the logon screen. »

Plasma Workspaces is the umbrella term for all graphical environments provided by KDE. Plasma separates components into "data engines" and their visualization counterparts. This is intended to reduce the total programming effort when there are multiple possible visualizations of given data; and to make it easier for the data engine and the workspaces to be written independently. Currently there are three workspaces being developed: Plasma Desktop for traditional desktop PCs and notebooks, Plasma Netbook for netbooks, and Plasma Active for tablet PCs and similar devices. »

GeekTool is an application for Mac OS 10.6+. It lets you display various kinds of information on your desktop via 3 default plug-ins:

XWidget is a free desktop customization platform. It’s light, handy with powerful visual widget editor and very subtle animations. The Android page is found here: http://android.xwidget.com/

GKrellM is a single process stack of system monitors which supports applying themes to match its appearance to your window manager, Gtk, or any other theme.

MiniUsage displays various data like CPU usage, amount of network flow, battery status and process names which uses much CPU time in a menubar. It takes little space and can display various data, so it's suitable for notebook.

Monitor numerous OS X statistics including: CPU activity System load over time Network bandwidth and activity Memory activity and usage Battery & wireless signal strength Disk usage Current time and date Compact, clever & fully customizable user interface Presents information both graphically and with text Beautiful on Retina display Fits in perfectly with the new system appearances Save & load custom appearances Minimizes impact on system performance View data on the desktop, in the menu bar or Dock Show & hide windows using system hotkeys »

Theme Widgets has eight small apps that run on your PC desktop. The apps cover different tasks such as: clock, calculator, weather, notes, calendar, timer, stopwatch and a whiteboard. This will hopefully grow over time.

BGINFO for X, also called BGINFO4X, is a clone of the popular program BGINFO for Windows created by Sysinternals.You can refer it as BGINFO for Linux, BGINFO for Unix, or BGINFO for X-Windows, which has derived to BGINFO4X (BGINFO for X).

This little application displays system information on your desktop in a similar way to some other desktop information tools. Unlike others, this application looks like wallpaper but stays resident in memory and continues to update the display in real time. Uses very little memory and nearly zero cpu. Perfect for quick identification and walk-by monitoring of production or test server farms. Everything is customisable including language.

WPInfo displays system information on the Windows wallpaper. It works similarly to BGInfo from SysInternals but it adds a few unique features:

gDesklets is an architecture for "desklets", which are tiny applets sitting on your desktop in a symbiotic relationship of eye candy and usefulness.