Hydrus - A personal booru-style media tagger that can import files and tags from your hard drive and popular...
TagSpaces - TagSpaces is an open source platform for personal data management. With TagSpaces you can manage and organize the files on your laptop, tablet or smart phone.
Danbooru - Danbooru is an advanced, tag-based image board system that is based on Ruby On Rails.
TMSU - TMSU is a tool for tagging your files.
Tabbles - Tabbles use tags to organize and find files along with your colleagues.
TAGXFS - Tagxfs is a semantic file system. It extends the user space file system to a tag based hierarchy.