7 embed an external website page in a node
An iFrame is the only option that doesn't involve huge amounts of work.

I guess if you really wanted to you you could write an API for the rails app that Drupal could consume and recreate the content off this data.

Technically you could get Drupal to scrape the HTML (file_get_contents or curl) of the ruby app and then cache this locally and embed in the node. This doesn't seem like a good idea as is inefficient and you may have problems with the search action and cache flushing mechanisms.