Rainmeter is a free Windows customization application. Empower your desktop with an expandable library of useful tools like handy notes, application launchers, weather, feeds and News Aggregator and system status.
RocketDock brings a Mac OS X Dock-style application launcher to Windows for free. With RocketDock, you can minimize apps to your dock to thumbnails, tweak any of your icons, view real-time window previews from the dock (in Vista), and quickly launch any app.
Samurize is a free system monitor and "desktop enhancement engine" for Windows. With Samurize, you can incorporate text files on your desktop and create custom desktop configurations and HUDs containing virtually any piece of information you’d like to see on your desktop.
4. Emerge Desktop
Emerge Desktop is a free Windows shell replacement that swaps out the default Windows taskbar, start-menu, and right-click menu with its own alternatives. As we said when we first covered it, Emerge creates a clean, minimalist desktop that’s great on its own or a perfect starting point for more customizations.
5. Auto Hotkey
AutoHotkey is an open-source scripting language for Windows. While the language itself is capable of a lot, customization lovers enjoy AutoHotkey’s ability to easily transform window transparency, add keyboard shortcuts to anything, and more.