JS Packaging, modeled after jammit but much lighter, and uses remote closure compiler.

compressor.rb

module Packager
  class Compressor
    
    attr_accessor :templates, :javascripts
    
    def initialize(config)
      @templates   = config['templates'] || {}
      @javascripts = config['javascripts'] || {}
    end
    
    def compile_javascripts
      compiled = @javascripts.keys.inject({}) do |hash, package|
        hash.merge!(package => @javascripts[package].map{ |file| read_file("#{Rails.root}/app/javascripts/#{package}/#{file}") }.flatten)
        hash
      end
    end
  
    def compile_jst
      
      namespace   = "window.JST"
      paths       = Dir["#{Rails.root}/app/views/**/*.jst"]      
      compiled    = paths.map do |path|
        contents  = read_file(path)
        contents  = contents.gsub(/\r?\n/, "").gsub("'", '\\\\\'').gsub("\t","")
        name      = template_name(path)
        "#{namespace}.#{name} = _.template('#{contents}');"
      end
      
      setup_namespace    = "#{namespace} = #{namespace} || {};"
      package_namespaces = [@templates.keys].flatten.compact.map{ |ns| "#{namespace}.#{ns} = #{namespace}.#{ns} || {};" }
      setup_namespace    = [setup_namespace, package_namespaces]
      create_closure([setup_namespace, compiled].flatten.join("\n"))
      
    end
    
    def compress!(data)
      response = Net::HTTP.post_form(URI.parse('http://closure-compiler.appspot.com/compile'), {
        'js_code' => data,
        'compilation_level' => "SIMPLE_OPTIMIZATIONS",
        'output_format' => 'text',
        'output_info' => 'compiled_code'
      })
      response.body
    end
    
    def create_closure(content)
      ["(function(){", content, "})();"].flatten.join("\n")
    end
    
    def read_file(path)
      File.open(path, 'rb') {|f| f.read }
    end
    
    def template_name(path)
      path = path.gsub("#{Rails.root}/app/views/", "")
      @templates.each_pair do |namespace, files|
        return "#{namespace}.#{File.basename(path, ".jst")}" if [files].flatten.compact.include?(path)          
      end
      return File.basename(path, ".jst")
    end    
  
  end
end

processor.rb

module Packager
  class Processor
    def initialize(app)
      @app = app
    end
  
    def call(env)
    
      return @app.call(env) unless env['PATH_INFO'].match(/javascripts/)
      package  = File.basename(env['PATH_INFO'], '.js')
      contents = []
      manifest = YAML::load(File.open("#{Rails.root}/config/packager.yml"))['javascripts']
      jsfiles  = manifest[package].map{ |filename| "#{Rails.root}/app/javascripts/#{package}/#{filename}" } || Dir["#{Rails.root}/app/javascripts/#{package}/*.js"]
    
      jsfiles.each do |file|
        lines = File.open(file,'r').map{ |line| line }
        contents << lines
      end
    
      [200, {"Content-Type" => "application/javascript"}, [contents.compact.flatten.join("\n")]]
    
    end
  
  end
end