Here's an easy way to keep track of the on-going changes to Ruby on Rails. The Rails team use the system Trac to manage their development and it includes a page to list all of the recent changes. While nice in theory, the fact that by default it shows changes to the development website too makes it a little confusing at first glance, so instead you can use/bookmark this link to see what is going on in the code itself:

• http://dev.rubyonrails.org/timeline?milestone=on&changeset=on