Common Tag

Common Tag is an interesting project, it is an attempt to create more linked data.

Common Tag is an open tagging format developed to make content more connected, discoverable and engaging. Unlike free-text tags, Common Tags are references to unique, well-defined concepts, complete with metadata and their own URLs. With Common Tag, site owners can more easily create topic hubs, cross-promote their content, and enrich their pages with free data, images and widgets.

It uses RDFa. There is a tool, Zemanta, to help embed Common Tags in weblogs.