What features do you expect from a tag based file manager?

I ask because Emacs Dired might qualify. It allows you to apply arbitrary “marks” to files, each mark is a single character. Some characters have special meaning, e.g. “D” means ready for deletion, and “*” is the default mark (not for deletion). You can then preform batch operations on marks, for example using marked files as arguments to a shell command.

However, without additional extensions, marks are not persisted between sessions, there is no virtual filesystem, and no search function for listing all files across multiple separate directories that match particular tags.

One such extension is filetags.el which is an Emacs UI inspired by the filetags file manager (which someone else already mentioned).