Tags for Mac

From CASEapps:

Tags allows you to manage your files in a way far superior to folders. Work faster, and be more efficient. Tags allows users to tag all their files on their Mac, such as files and folders in the finder, emails in Mail, photos in iPhoto, bookmarks in Safari, etc.., directly from within the application. It allows the user to associate files of different types to one another with ease and without creating duplicates. Users can apply many different tags to a single file, as well as apply the same tag to multiple files. This allows users to associate files to one another in a way far superior to a rigid file / folder structure. With Tags, users can quickly find files irrespective of file type or where they were saved. Tags can be invoked with a simple keystroke in most applications so that users can Tag files and search for Tags, wherever they are.