Featureserver
From Wildsong
Tutorial
http://www.paolocorti.net/2008/02/21/a-day-with-featureserver-1/
Corrections to tutorial: svn URL is http://svn.osgeo.org/featureserver/trunk/
James Fee blog post
http://www.spatiallyadjusted.com/2008/02/05/bringing-open-source-gis-into-an-esri-shop/