This is a template prototyping app in Sinatra. Dirt simple, but hey.

config.ru

require 'preview'
require 'rack'
 
run Sinatra::Application

preview.rb

#!/usr/local/bin/ruby

require 'rubygems'
require 'haml'
require 'compass'
require 'sinatra'

set :app_file, __FILE__
set :root, File.dirname(__FILE__)
set :views, 'views'

configure do # if you don't want to use compass this can go
  Compass.configuration do |config|
    config.project_path = File.dirname(__FILE__)
    config.sass_dir     = File.join(Sinatra::Application.views, 'stylesheets')
    config.http_images_path = "/images/"
  end
end

get '/' do
  haml :history # this is just the default page - change :history to a different file if you want a different default
end

get '/:name.html' do # if you want a different prefix - or no prefix - change .html here
  haml :"#{params[:name]}"
end

get '/stylesheets/:name.css' do
  content_type 'text/css'

  sass :"stylesheets/#{params[:name]}", Compass.sass_engine_options # if you don't want Compass, comment this out
end

Rakefile

require 'haml'
require 'compass'
 
 
build_ns = namespace :build do
  task :haml do
    
    Dir["views/*.haml"].each do |haml_filename|
      puts "Processing #{haml_filename}..."
      haml = IO.read(haml_filename)
      html = Haml::Engine.new(haml).render
      File.open("compiled/#{File.basename(haml_filename).sub("haml", "html")}", "w") {|f| f.write(html)}
    end
  end
  
  task :sass do
    Compass.configuration do |config| # remove this block if you don't want compass
      config.project_path = File.dirname(__FILE__)
      config.css_dir = "/stylesheets"
      config.sass_dir = "views/stylesheets"
      config.images_dir = "public/images"
      config.http_images_path = "/images"
      config.javascripts_dir = "/javascripts"
      config.output_style = :expanded
      config.sass_options = {:line_comments => true}
    end
    
    
    Dir["views/stylesheets/*.sass"].each do |sass_filename|
      next if File.basename(sass_filename)[0,1] == "_"
      puts "Processing #{sass_filename}..."
      sass = IO.read(sass_filename)
      css = Sass::Engine.new(sass, Compass.sass_engine_options).render # remove compass.sass_engine_options if you're using Compass
      File.open("compiled/stylesheets/#{File.basename(sass_filename).sub("sass", "css")}", "w") {|f| f.write(css)}
    end
  end
end
 
task :default => [build_ns[:haml], build_ns[:sass]]