I don’t know if this qualifies as a GTD (Getting Things Done) tool, but I would like to call it that because it makes things easy for me. I have always preferred to have a clutter-free desktop and this "Layered Desktop" not only does keep it neat but also a bit more focused and productive.
You can use it to organise your icons in groups, like:
the paper area for work stuff;
the aluminium plate for personal projects;
the wooden desk for yet to be categorised elements, like finished or in-progress downloads.
the post-it for urgent elements (I usually have the files I am currently working on in here).
Download the high-res file and instructions on how to fit it to your desktop.