What does HackerNews think of tag?
A command line tool to manipulate tags on Mac OS X files, and to query for files with those tags.
Language:
Objective-C
Here is a command line based tag system for Mac osx - https://github.com/jdberry/tag - using xattrs
You can 'brew install tag'[1] and manage them in metadata, which will also expose them in Spotlight, sorting in Finder etc. (but not so handy across OSes)
For macos I feel like https://github.com/jdberry/tag is probably a better solution.