Drupal and Ruby on Rails
Because I'm a fan of both Ruby on Rails and Drupal (yes, Drupal uses PHP), I get a surprising number of visits to my website each day from Google searches that include some combination of the two as keywords. I find this strange because if you know either of the two, you know that they're in two totally separate worlds.
Drupal doesn't expose any kind of API (besides RSS feeds) that Rails could take advantage of, nor does it make sense to create one.
Since Drupal uses PHP, you can't create module for it in Rails. The only way I could possibly think to marry the two would be to create a module that simply puts an iframe on the page and loads it with your Rails app. In fact, it doesn't even have to be a module. It could be a simple page you create with an iframe pointing to your Rails app.
But why in the hell would anyone want to do this? I guess I'm a little short sighted on this issue right now as its hard to see where the two would play nicely with each other, or why you would want them to. If you want to extend Drupal, use PHP. If you want to use Rails, look at Mephisto or Radiant CMS and extend either of those.
This could just be a case of people not fully understanding what the two are. For those people, Drupal is a CMS written in PHP. Ruby on Rails is a web framework that allows you to easily create web applications. I could see how some people might also think of Drupal as a framework to base a web application off, but again, if you're going to start with Drupal, you will need to know PHP to modify it.
Am I missing something here?