Sinatra[1] is more like Flask. From your list Rails has an ORM (ActiveRecord) and built in ActionView form helpers, but no default admin interface or authentication. The standard authentication library in the community is usually Devise[2]. What ‘etc’ includes is difficult to comment on :)

[1] http://sinatrarb.com/

[2] https://github.com/plataformatec/devise

Not at all. The ruby equivalent to Flask is Sinatra: http://sinatrarb.com

Rails and Django are equivalent to each other from the sense of providing an MVC based framework to build a web application.

No. Sinatra [1] is more like Flask.

Rails has session management, forms, ORM, and simple authentication all built in (as well as asset compilation, schema migrations, websockets, asynchronous processing, file uploads, etc). Models do not contain schema definitions, they're defined elsewhere. Admin functionality needs to be added.

I've got some experience in Python at this point if I were to build a new CRUDy business app I would use Rails because of my familiarity with Ruby and Rails. If I wanted to learn more Python as a main goal I'd pick Django.

[1] http://sinatrarb.com/

Django is not the best solution if your goal is to learn Python -- it simply has too many magic going on underneath, and some of their solutions are convoluted due to its specific architecture and backward compatibility requirements.