Yii Modules in Craft, samples? Does anybody know of a collection or library of Yii Modules online?

I'm trying to understand how easy they can be moved from one application to another, are we going to see something similar to the plugin store for modules within Craft? :O
In the context of Craft CMS, Modules typically would be used for adding functionality to the website itself. As such, you'd use it for things that are specific to that project. Check out the article Enhancing a Craft CMS 3 Website with a Custom Module for details.

You can also generate your module scaffolding via pluginfactory.io