Try it at https://serene-shelf-42005.herokuapp.com/admin
See https://serene-shelf-42005.herokuapp.com/admin/issue/nestable
See, for example, https://serene-shelf-42005.herokuapp.com/admin/blog_post/history. With login/logout configured if will associate changes with the logged in user.
rails_admin integrates with a couple different rails authentication and access management gems - limiting access by model or field looks pretty straightforward.
rails_admin_import (https://github.com/stephskardal/rails_admin_import) was probably the coolest plugin I tried. Importing the issues taxonomy and associating the terms with the right blogs posts via a many-to-many relationship was easy.
The admin UI was pretty easy to configure and seems quite flexible. I think the default multi-select widget is clunky, but it doesn't looks too hard to swap it out for something better.
Non-admin pages work like plain old rails - get the content in a controller and template it in views.
Provides multilingual content useing the globalize gem (https://github.com/globalize/globalize) and an integration with the rails_admin gem (https://github.com/scarfaceDeb/rails_admin_globalize_field)