This month Nick Mulder is coming to educate us about Rack (http://rack.github.io/):
Rack is Lego
Lego is great, given the right pieces you can build anything. Rack is lego for the Ruby driven web, given the right pieces you can build anything. You may think this is overselling Rack; perhaps you need to come to see this for yourself. We will start the basics and work our way up to some tricky Rack apps with questionable middleware stacks. Rails should be considered by all to be a tricky Rack app with a very questionable middleware stack, so expect plenty of details on how Rails takes you from request headers to your router/controller and back to a status code, more headers and a body.
Bio - Nick Mulder ( http://twitter.com/nickmulder )
Nick has been making a living off Rails/Ruby since 2005, he loves web tech despite all its nasty bits. In his spare time he makes large pieces of wood smaller and enjoys long walks on the beach with his wife and 3 kids.