NOTE -- as of August 2006 it looks like this service is shutdown. From the site: With the web services interface, you can plug Tagyu into your own programs. Add tag suggestions to your favorite blogging tool. The API uses a simple REST query. If you want to get suggested tags for a peice of content, you simply tack that content to the end of a URL and you'll get an XML document with the suggested tags.
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There are no mashups, developers or code associated with this API yet.
Tagyu's been shut down for now :(