177-model-versioning is a project mainly written in RUBY and JAVASCRIPT, it's free.
Railscasts Episode #177: Model Versioning
http://railscasts.com/episodes/177
Commands
sudo rake gems:install script/generate vestal_versions_migration script/generate migration version_existing_pages rake db:migrate
script/console
p = Page.all p.versions p.revert_to(7.minutes.ago) p.content p.revert_to(:last)