Windows only: Application launcher 7stacks adds the Stacks functionality of Mac's OS X to Windows 7, including Aero transparency effects that blend into your taskbar perfectly.
To create your own stacks, launch the application, pick a folder and the type of launcher you want, create a shortcut on the desktop, and then right-click the shortcut and pin it to the taskbar. You can pin up to 10 shortcuts onto the taskbar this way, and you can choose between Menu, Grid, or Stacks (pictured). You don't have all of the functionality that the latest version of StandaloneStack gives you, but it blends into the desktop really well with the Aero transparency effects, making it well worth a look for anybody using Windows 7.
7stacks is a free download for Windows 7 only. For more, check out how StandaloneStack is an awesome file-browsing widget, or out other favourite methods of consolidating taskbar launchers with Jumplist and switching folders with Folder Menu.