I am not sure what kind of applications you are looking for, but in general there are thousands of successful and big sites out there... for instance look at the sugar network, its based on Drupal

also if you mean built on CMS out of the box, I don't either, and you will have to customize it in order to make something useful, but the point is that with RoR you have to pretty much build from scratch whereas with other CMS like Drupal you already have many functionalities included in the core and you don't have to really reinvent many things, you just customize or add the ones you want