I need a way of assigning tags and numbers (like rating, importance, etc) to my files and also be able do queries and file operations based on these metadata. Just like a photo management software (e.g. F-spot) but for documents (PDF, DJVU, EPUB, etc).
This can be a file manager with extra abilities or a file indexing system. The only thing I've found so far is recoll however it doesn't allow me to assign tags to files.
By the way, I've been using XFCE for quite a while so if Gnome has such a software built-in, I may not know about it.