Exactly when did federated wiki begin? GitHub has the first commit: github 
readme as challenge
WardCunningham
Smallest Federated Wiki Goals ============================= Demonstrate that wiki would have been better had it been effectively federated from the beginning. Explore federation policies necessary to sustain an open creative community.
Client Goals ============ Offer to a user a browsing experience that is independent of any specific server. Support writing, editing and curating of one server in a way that offers suitable influence over others.
Server Goals ============ Encourage the deployment of independently owned content stores. Support community among owners through systematic sharing of content.
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When did I join the federation?
2012-07-04 when wired ran a story? wired
2014-06-12 in Jon Udell's earliest fedwiki article? blog
2015-09-13 my first contribution of code making calendar plugin collaborate with method plugin: pull request
2015-08-16 first edit of my first wiki? rev30