_tree.html.erb

<!-- partial -->
<% content_tag :li, :id => dom_id(root) do %>
    <%= content_tag :span, root.name %>
    <%content_tag :ul do %>
        <% for child in root.direct_children do %>
            <%= render :partial => "tree", :locals => {:root => child}%>
        <%end %>
    <%end unless root.direct_children.empty? %>
<%end%>

index.html.erb

<!-- index view -->
<h1>Items</h1>

<ul id="my_item_tree">
    <%= render :partial => "tree", :locals => {:root => @root} %>
</ul>

<%= sortable_element_reporting_target "my_item_tree", "moved_item_id", 
                                      :tree => true,
                                      :url => sort_items_path, 
                                      :method => :put  %> 

item.rb

# Model
class Item < ActiveRecord::Base
  acts_as_nested_set
end

items_controller.rb

# Controller
class ItemsController < ApplicationController
  handles_sorting_of_nested_set
  
  def index
    @root = Item.find_by_parent_id(nil)
  end
  
  def sort
    new_position = position_of(:moved_item_id).in_tree(:my_item_tree)

    # This is where you should update your model and 
    # return som javascript to update the view.
    # In this sample, we settle for logging the new position and rendering nothing.
    logger.info("New position of item #{params[:moved_item_id]}: " + new_position.inspect)
    render :nothing => true
  end

end

routes.rb

# routes.rb
ActionController::Routing::Routes.draw do |map|
  map.resources :items, :collection => {:sort => :put}
end

styles.css

ul { 
	list-style: none; 
}

li > ul { 
	padding-left: 1em; 
}