Modules (or Drupal 7 module-equivalent features) added to core in Drupal 8

Module (or feature)	Notes
Action	Drupal 7 action
Ban
HTTP Basic authentication
Breakpoint
Caption filter (part of `filter` module)	Drupal 8 ships with the ability to align and caption images, videos, blockquotes and so on. The implementation is based on Drupal 7's Caption Filter module.
CKEditor (`ckeditor`)	Makes the Drupal 7 contrib CKEditor module obsolete, but comes with a vastly simpler & better configuration UX, and much deeper integration.
Configuration Translation module	Successor to the Internationalization module as well as several glue modules from Variable, Internationalization views, Webform localization, etc..
content_translation
CTools	The CTools plugin system has been replaced by the Drupal 8 Plugin API. The CTools object cache is now replaced by the Drupal core TempStore. CTools Dependent is replaced by the Drupal 8 (and Drupal 7) Form API #states. Drupal core now supports modal dialogs, replacing CTools' modal dialogs. (More on the Drupal 8 modal API.) All CTools functionality that Views relied on is now superceded by Drupal 8 core functionality. (Also see the Drupal 8 Page Manager project.)
Entity Reference module
Date module	Provides the field type and a light API. No recurring dates or calendar functionality.
Text Editor (`editor`)	A better integrated version of the WYSIWYG module that incorporates only the essentials.
email	There's email field with widget and 2 basic formatters in Core
entity
entityreference
entitycache
hal
history
language
link
menu_link
migrate
migrate_drupal
number
options
Quick Edit (`quickedit`)	Provides in-place editing of entity fields. Has a Drupal 7 backport named Edit module.
Responsive Image (`responsive_image`)	Formerly Picture in contrib.
rest
serialization
telephone
text
tour
Views	The most popular Drupal module was added as well as conversions of several blocks and lists to Views (including administration pages).
Views UI
xmlrpc