Usage:

script/plugin install git://github.com/brynary/rack-bug.git 

# config/environments/development.rb
config.middleware.use "Rack::Bug"

# add bookmarklet to browser
open http://RAILS_APP/__rack_bug__/bookmarklet.html

Thanks to:

Django debug toolbar
Rails footnotes
Rack's ShowException middleware
Oink
Rack::Cache