A simple mechanism for P2P InterWiki:

* CategoryCategoryCategory would be a collector of SisterSite wikis' CategoryCategory pages. 
* CategoryBacklinkSearching would GoogleScript to search for all SisterSite pages within a given category.
* The SisterSite logos would visually disambiguate the resulting links. Each SisterSite would serve its own SiteLogo''''''s.
* Once someone put together the requisite GoogleScript all the WikiServer would do would be to serve the search page; the script would do all the google-interaction, aggregation and reporting work on the client machine.

On the other hand maybe it should just be BacklinksAsInterWiki? --PeterMerel

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See PagesAsInterWiki