TMSU - TMSU is a tool for tagging your files.
Hydrus - A personal booru-style media tagger that can import files and tags from your hard drive and popular...
Danbooru - Danbooru is an advanced, tag-based image board system that is based on Ruby On Rails.
Dantalian - Dantalian is a set of Python scripts to help with file organization and tagging with hard links.
Tagfs - tagfs is Fuse file system to organize your files using tags.
TAGXFS - Tagxfs is a semantic file system. It extends the user space file system to a tag based hierarchy.