Rails will be retrofitted to make it easy to start with a “core” version of Rails (like Merb’s current core generator), that starts with all modules out, and makes it easy to select just the parts that are important for your app. Of course, Rails will still ship with the “stack” version as the default (just as Merb does since 1.0), but the goal is to make it easy to do with Rails what people do with Merb today.
Rails will be retrofitted to make it easy to start with a “core” version of Rails (like Merb’s current core generator), that starts with all modules out, and makes it easy to select just the parts that are important for your app. Of course, Rails will still ship with the “stack” version as the default (just as Merb does since 1.0), but the goal is to make it easy to do with Rails what people do with Merb today.
http://yehudakatz.com/2008/12/23/rails-and-merb-merge/