ruby-on-rails-3 - 在 Rails 3 中构建 Gem、插件或引擎

Answer 1

Enginex is included in rails 3.1. There’s no need to use it as a gem anymore on new applications !

This is just telling you that before rails 3.1, you had to include the enginex gem to create rails engines. This is not true anymore for rails 3.1 and higher.

All your questions are answered here.

Basically, Engines are pretty much like Rails applications. In fact, a Rails application is an Engine in someways. Engines can be "mounted" into others Rails applications (Devise for example). Engines include full MVC architecture for you to play with. Whereas Gem are not meant to include controllers, views and routes. Gems are meant to add new functionality to Ruby.