Ruby on Rails
Builder

http://builder.rubyforge.org/

require 'rubygems'
  require_gem 'builder', '~> 1.2'

  builder = Builder::XmlMarkup.new
  xml = builder.person { |b| b.name("Jim"); b.phone("555-1234") }
  xml #=> <person><name>Jim</name><phone>555-1234</phone></person>