Erik Moeller wrote:
Dear community,
after the terrorist attacks on September 11, 2001, Wikipedia was overwhelmed by people expressing their sympathy for the victims, adding material about affected organizations, and generally flooding us with content that was inappropriate. Rather than turning these people away, the decision was made to set up a separate wiki, sep11.wikipedia.org, which still exists today.
At the time these pages were very much a part of Wikipedia; the separate wiki was created a year later as a place where they could be archived after a number of people started deleting them from English Wikipedia.
-- brion vibber (brion @ pobox.com)