Francis gave a very interesting talk about his new Rails search engine plugin, which is called acts_as_xapian. Francis also covers some of the sites he's been using xapian on, such as WhatDoTheyKnow.
Act As Xapian
Francis uses open source software to hack democracy. That is, to provide tools to make it easy for anyone to be an activist. He’s currently working on WhatDoTheyKnow in Ruby on Rails.