Modules. You practically cannot master Drupal without them. They extend and customize Drupal functionality. It's true that some are still not converted properly to the newest version and some are poorly or not maintained at all. But there are many who solve your everyday problems efficiently. Therefore, we will look at the most popular Drupal modules according to the official website of Drupal.
Chaos tool suite (ctools) is the most popular Drupal module, with almost nine hundred thousand sites using it, making it the most installed Drupal module. This module is a set of tools to improve the developer experience. The tools are, for example, Plugins, Exportables, Contexts, AJAX responder ... It also has a Page Manager, whose job is to manage panel pages. The latest version for Drupal 8 is 8.x-3.0, while for Drupal 7 it’s 7.x-1.12.
The next one is in Drupal 8 core. It is Views, which therefore needs to be downloaded only for the Drupal versions 6 and 7. You need this module if you want to, for example, alphabetically sort the default taxonomy view, sort the default front page view differently, want to provide 'unread forum posts', don’t like the way articles are displayed in the article module and so on.
The third most popular Drupal module, which still has more than eight hundred thousand sites using it, is Token. It provides UI for browsing tokens and additional tokens not supported by the core. It’s available for version 8.x-1.0 and 7.x-1.7.
If you have ctools and Token, you can have Pathauto. It’s a module, which automatically generates URL aliases for various kinds of content, like nodes or taxonomy terms. This means that users don’t have to manually specify the path alias. The version for Drupal 8 is the same as for Tokens, while the available version for Drupal 7 is 7.x-1.3.
Libraries API is the next one and you can say that it’s the denominator for all Drupal modules that integrate with external libraries. It’s the first module, which is installed in a little less than seven hundred thousand sites. Although Drupal 8 core introduced some improved library management tools, Libraries API remains an important API module for the Drupal 8 contrib environment.
In order to deal with entities and their properties, you need Entity API. It provides API functions allowing modules to create, delete, view, save or to determine access for any entity. There are still more than six hundred thousand sites using this module. Entity API for the newest version of Drupal will someday be moved to Drupal core, but until then it is still used as a module.
One more absent from Drupal 8 is jQuery Update, a module which, the name says it all actually, upgrades the version of jQuery in a Drupal core.
We’ll conclude our list with the one, very helpful to the newcomers. Administration menu provides an administration interface or to be easily understood navigation. But be careful! The project is not covered by Drupal’s security advisory policy, so in case you use it, it will be at your own risk.
You can find more of the most popular Drupal modules here.