TaggTool - The Personal File Tagging Utility.
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.
Elyse - The free version allows up to 30 tags.
allTags - allTags is a free, tag based file management application.
miTaggedMarks - With miTaggedMarks you organise and access your local bookmarks using tags, instead of the usual hierarchical tree structure. With a new way to handle a large number of tags. Works with nearly any browser.
TMSU - TMSU is a tool for tagging your files.