Essential module for developers. Should be disabled in production environments.

"Module provides Drupal installation with various security hardening options. This lets your mitigate the risks of exploitation of different web application vulnerabilities."

"The Security Review module automates testing for many of the easy-to-make mistakes that render your site insecure."

The WYSIWYG module is my favorite for rich text editing in Drupal 6 and Drupal 7. (In Drupal 8, WYSIWYG is in core.) Here's how I set it up.

Provides a super fast and feature-packed administration navigation menu.

The Features module allows you to export configuration to code in an easy way.

This module is essential for configuration management in Drupal 8

For Drupal 8, adds the ability to add CSS classes to link fields.

The best part about this module is that each role can have a default text format.

Drupal 7 core allows for reordering the formats in the UI, thus picking a default too. However, there is no role based ordering, as there is with the Better Formats module.

This Drupal 8 module allows to restrict text formats on fields.