ccMixter tracks in-community mixversations. We’ve now released a very simple beta API that allows tracking remix relationships across sites. The API is implemented in ccHost, the GPL software that runs ccMixter, and you can implement it for your site. For details see ccMixter developer Victor Stone’s blog entry and the beta documentation. Feedback to the cc-devel list.
In other ccHost development news, the excellent Open Clip Art Library is in the process of migrating to ccHost and doing some work along the way to make it easy for others who want to use ccHost for non-music remix communities to do so.