You are probably familiar with the form helper collection_select. It is a helper that returns a <select> element and <option> tags for a given collection. In Rails 4, collection_check_boxes and collection_radio_buttons have been added to help with has_many association assignments.

Over two years ago, David Lee submitted a pull request which mapped the PATCH HTTP verb to update controller actions to follow proper REST semantics. This change is finally making its way into Rails as of version 4.0.

In Rails 4, a new pattern has been introduced to secure your models from mass assignment. You can filter the parameters passed to your model in the controller instead of whitelisting attributes in your model using attr_accessible.

One of the new features in Rails 4 is the ability to suffix controller-wide information to ETags. At the controller class level, you can set data by passing a block to the new `etag` macro style method. The etag method can be called multiple times, with each subsequent call suffixing the information to the response's ETag for easy client-side caching.

As of Rails 4, page and action caching has been removed from the framework. While they are no longer available out of the box, each feature has been extracted to a gem. Both page and action caching can be restored in Rails 4 applications by including the actionpack-page_caching and actionpack-action_caching gems in your Gemfile respectively.