Dirty_after_save is a project mainly written in Ruby, it's free.
Track changes even after saving an ActiveRecord model
This simple gem adds support to all ActiveRecord models in your application to track the changes made to a record before it was saved. Standard Rails forgets this information as soon as save is called.
To access all changed attributes after save has been called, use
Model#changed_attributes_before_save
To access changes in individual fields, append the suffix '_change_before_save', i.e.
Model#field_change_before_save
To figure out if a field was changed, append the suffix '_changed_before_save?', i.e.
Model#field_changed_before_save?
That's it. Enjoy.