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.
Tabbles - Tabbles use tags to organize and find files along with your colleagues.
allTags - allTags is a free, tag based file management application.
Elyse - The free version allows up to 30 tags.
TMSU - TMSU is a tool for tagging your files.
Danbooru - Danbooru is an advanced, tag-based image board system that is based on Ruby On Rails.