How do you develop a web application in Eiffel?
Is there a webapp framework for eiffel?
Are there examples of web apps developed with eiffel?
There have been many, but the most widely framework currently supported is the Eiffel Web Framework. Frameworks in Eiffel tend to focus more on plumbing, i.e. fastcgi support, routers, validation. We miss the breadth of CMS frameworks PHP has for example.
So if you're looking for Drupal in Eiffel, nope, there is nothing like that. There's a lot of stuff developed in Eiffel, but usually it's business, and specific. A common approach would be a ExtJS front-end, and Eiffel fastcgi back-end.