Tabbles - Tabbles use tags to organize and find files along with your colleagues.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Elyse - The free version allows up to 30 tags.
allTags - allTags is a free, tag based file management application.
TaggTool - The Personal File Tagging Utility.
TMSU - TMSU is a tool for tagging your files.