Rainmeter is a fully customizable resource monitor for Windows

http://rainmeter.net/RainCMS/?q=Rainmeter101

Rainmeter is a fully customizable resource monitor that allows you to monitor vital system information including memory usage, disk usage and utilization, network traffic, uptime and many other details. You can also choose to monitor weather conditions, RSS feeds, Twitter activity, Gmail and various other online resources. Rainmeter is highly customizable and can be configured to display as much or as little information as you want, however it requires you to tinker with .ini files and tons of individual settings, so it may not be for everyone.

What is Rainmeter?

Rainmeter is an application which will allow you to place what are called "Skins" on your desktop. These skins can measure and display a wide variety of information. Some examples of things you can display are:

• System Information - CPU, RAM, Network, Drive Space, you name it...
• Launchers and Docks - Be creative and create your own RocketDock or launcher
• Music and more - Interfaces for WinAmp, iTunes, and more
• Web-based content - Weather, GMail inbox, RSS feeds. Just about anything you can parse from the web

Skins are fully customizable by you. They are primarily just .ini text files with simple commands that say "Measure this, and display it here looking like this". We will get into customizing skins more later, but you can use all your creativity and very simple Rainmeter statements to really make your desktop your own!

What isn't Rainmeter?

• Rainmeter is not WindowBlinds(tm). It does not have any ability to change in any way your Start Menu, Taskbar, Notification Area (artist formerly known as System Tray) or any other Windows elements.
• Rainmeter does not manage your Desktop Background (Wallpaper). All those cool skins you see on DeviantArt or Customize.org may or may not come with the displayed wallpaper in the download, but in any case it is up to you to load them with the normal Windows routines. Rainmeter is not Display Fusion.

Installing

Download the latest release or beta version from Rainmeter.net. You may download and run the installer (.exe) version or manually install with the "portable" (.zip) version.

Rainmeter is fully Windows Vista / Windows 7 compatible. The file which Rainmeter uses to keep track of the skins you have loaded and how they are configured (Rainmeter.ini) is now in your "Application Data" folder, and all Rainmeter "skins" are stored in your "My Documents" folder. This means that you do not have to run Rainmeter as an "Administrator" or worry about conflicts with UAC (User Account Control).

Rainmeter automatically installs the suite of skins "Enigma" by Kaelri as well as the "RainBrowser" skin manager and "RainThemes" themes manager by JSMorley.

Default file locations:

The Program:
Windows XP: C:\Program Files\Rainmeter
Windows Vista & Win7: C:\Program Files\Rainmeter

Your "Skin" files
Windows XP: C:\Documents and Settings\YourName\My Documents\Rainmeter\Skins
Windows Vista & Win7: C:\Users\YourName\My Documents\Rainmeter\Skins

Rainmeter.ini and your "Themes"
Windows XP: C:\Documents and Settings\YourName\Application Data\Rainmeter
Windows Vista & Win7: C:\Users\YourName\Appdata\Roaming\Rainmeter

More information on installing Rainmeter is available in the Rainmeter Manual at Rainmeter Installation

Rainmeter Terminology - An Overview

Let's talk a bit about how the terminology for the various components of Rainmeter should be referred to. Truth be known, there is no one perfect way, as different folks using Rainmeter for any length of time have evolved their own ways of referring to things, and there is no "set in concrete glossary" for Rainmeter. However it does help, especially when asking for help on the forums, to have a common understanding of what things mean.

The organization is defined by these somewhat hierarchical terms:

->Suite
-->Config
--->Skin
---->Variant

Suite
A set of configs, normally in a single folder and many subfolders under \Skins, which have a single author and a common theme or style.

Config
A folder, which may or may not have subfolders, under \Skins which contains one or more skins.

The only real difference between a "suite" and a "config" is that normally a suite is by one author, has a common style, and may include shared variables or even a tool to help user set attributes common to all the skins in the suite. A config is a folder of skins. It's how Rainmeter organizes things on the context menu.

Skin
The contents of a single folder, which has one or more .ini "skin" files. For all practical purposes, when you say "skin" you generally mean "a .ini file".

Variant
As only one .ini file per folder can be loaded by Rainmeter at a time, a folder containing two or more .ini files is considered one "skin", with some number of "variants". An example is a clock config folder with "Clock12Hr.ini" and "Clock24hr.ini" where loading one unloads the other automatically.

What about Themes?
"Themes" are not a part of the Rainmeter application proper, but are a term used by the addon application RainThemes, which is installed as a part of the Rainmeter installation. What RainThemes does is allow you to save your current Rainmeter setup; the skins, their locations and settings, and even your current wallpaper, in a text file (really just a copy of Rainmeter.ini) which can be loaded if you want to get back to a particular setup on your system. A "Theme" does not actually contain the skins or in fact any files at all, it is just a way to tell your copy of Rainmeter to put things back to a saved state.