visualize rails api

I am looking for ways to better understand the rails api.

I found a tool used by Drupal that visualizes the drupal api in a graph that demonstrates the relationship between methods calling one another.

See a screencast on it:

The value I saw in it was that it increased the clarity of how methods relate to one another. When I debug rails (have been using Netbeans to do this), it's hard to track when new files are opened and the overall flow is difficult to track as method calls move across the framework.

Is there any similar tool for Ruby or Rails? Or any other type of approach that might help me better navigate the API?