Comment by joshbuddy

Essentially, it let's you take something like

  before '/blog/:id' do
    @blog = Blog.get(params[:id])
  end
  
  get '/blog/:id' do
    @blog
  end
  
  put '/blog/:id' do
    @blog.update_attributes(params)
  end

and turn it into

  path 'blog' do
    var do |id|
      @blog = Blog.get(id)
      get { halt @blog }
      put { @blog.update(request.params); halt :ok}
    end
  end

I feel this is DRY'er than the Sinatra representation. It also has nice integration with Rack itself. The implementation is very simple, easy to get into.