First, a disclaimer that I haven't worked with the Windows Library function, so if I've missed some major benefit or function, I apologize. As others have stated, Mac OS X doesn't currently directly support (what I would call) collections of filesxe2x80x93groups of files related by user-defined criteriaxe2x80x93directly. (Technically of course, a "folder" fits into this definition, but, ignoring aliases for the moment, a file can only live in one folder collection.)
A few years back Lifehacker posted Metadata as a 'filing system'. The idea is, in essence, to tag all of your files and use Spotlight and Smart Folders to find and "organize" those files.
On a smaller scale, I keep many of my text files in Yojimbo and use it to create collections. My writing workflow is now plaintext/markdown based, so Yojimbo is an archive of my writing. Once I drank the kool-aid, Yojimbo reduced my Documents folder, and it's hierarchy, significantly.
Yojimbo doesn't work for all file types though. EagleFiler brings many of Yojimbo's features to the Finder and can be applied to different file types. The caveat being that of these programs build a database of your files and you have to manage the files from within the software UI.
Enter Yep which uses OpenMeta tags, allowing you to move, copy and delete files freely using the Finder. Yep seemingly provides much of the functionality, flexibility and convenience of the Microsoft Library with the least imposition on workflow.
OpenMeta is an OS X Cocoa Objective - C technology that allows any application to read and or write tags, ratings, etc to any file. It works with 10.5 and 10.6
The idea of the project is for commercial, open source and in house programs to be able to use OpenMeta for reading, writing and dealing with user defined meta data. The metadata is stored in extended attributes (xattr).
Some of the metadata stored can be stored in such a way so as to trigger the Spotlight indexer to add the data to the Spotlight DB, allowing it to be searchable.