Tags
Extend your Finder with tags, to find your files in multiple ways.
...Create new Tags by duplicating and renaming the Mother Tag. Drag your file or folder on top of a Tag icon to add it to that Tag. Double-click a Tag to view all items that you added to it. Remove items from a Tag by dragging them to the Trash. Or remove the Tag itself by dragging it to the Trash. Tags are just like folders in many ways; you can even tag Tags!
The software works on Mac OS X 10.4 and all higher versions. Have a look at the screenshots to inspire you, and make sure to read the Readme that is included with the download, because it's really helpful.