ActiveRecord doesn't generate models based on database tables, it uses conventions on table and attribute names along with Ruby's metaprogramming capabilities to define behaviour on models automatically. From my understanding, Cayenne requires manual mapping of the database to your models, which is done via XML files that are either handwritten or generated by their GUI application and have to be regenerated on every database change. That's a far cry from the ease of use of ActiveRecord. How you value that ease of use versus your desire for static typing is up to you, but they’re not comparable from a functionality point of view.

And like I said above while you might be able to recreate some of Rails' functionality in other languages, you wouldn't be able to replicate all of it with the same fluidity and readability that you have in Rails