$ gem install kitsune --source http://gems.github.com

$ script/generate kitsune --include-page-model

Other options supported:
--without-page-model Exclude Page Model
--without-user-model Exclude User Model
--versioned Setup versioning for ActiveRecord, will need vestal_versions preinstalled

$ rake db:migrate

$ script/server

Then go to:
http://localhost:3000/admin/kitsune
Lo and behold, admin UI is automatically created for all models defined in the rails application.

Cherry pick from the commands below to add functionality to the admin interface:
display, edit, display_and_edit, no_menu, name, category, order_by, disable,sortable, file, image, multipart, select, string, text, sit, no_edit

@class Product < ActiveRecord::Base
  has_and_belongs_to_many :product_categories
  has_many :product_photos
  has_many :voltage_ratings

  admin do
    display_and_edit :short_name
    edit :long_name, :product_category_ids, :description, :overview, :features, :order
    wysiwyg :description
    wysiwyg :overview
    wysiwyg :features
    collection_select :product_category_ids, ProductCategory.all, :id, :title, {:include_blank => true}, {:multiple => true}
  end

  def self.search_results(keywords)
    Product.all(:conditions => ["(products.short_name like :search or products.long_name like :search or products.description like :search)", {:search => "%#{keywords}%"}])
  end

  def to_param
    "#{id}-#{short_name.gsub(/[^a-z0-9]+/i, '-')}"
  end
end@

And that is how you do it.