Just forwarded to my by Frank Osterfeld:
Announcing Leaftag, our desktop tagging framework. This is an evolution of the original prototype we created, originally named fstaglib (isn’t leaftag just so much better?).
The main part of Leaftag is a library called (oddly enough) libleaftag, which interfaces with the tag database. It’s GObject-based, and the API is quite small. It can tag anything with a URI.
There’s tagutils, a small app used for working with tags and files. It is able to tag and untag files, list all known tags, list all files with a specified tag, and manipulate tag properties (such as icons and descriptions). It also includes some symlinks that provide shortcuts to common tagutils functions (tag, untag, tagls, tags, and tagprop).
leaftag-python contains Python bindings for libleaftag. It simplifies the already simple libleaftag library.