The Smallest Federated Wiki was the founding project that has grown into many sites running substantially evolved client and server software. See Federated Wiki wikipedia 
From WIRED magazine :
> Ward Cunningham, the creator of the wiki, is proud of his invention. But there is one thing he regrets. The central idea of a wiki -- whether it's driving Wikipedia or C2 -- is that anyone can add or edit a page, but those pages all live on servers that someone else owns and controls. Cunningham now believes that no one should have that sort of central control, so he has built something called the federated wiki.
See Linked Data