Rails vs Web2Py compares the popular web frameworks Ruby on Rails and Web2Py. Some key differences include: - Controllers are defined as classes in Rails and functions in Web2Py. - Routing is defined in a routes.rb file in Rails and routes.py in Web2Py, which supports reversed routing and regex. - Views use ERB templates in Rails and native Python templates in Web2Py. - Web2Py has built-in support