Comparison of Menu API in Drupal 7 and 8
Drupal 7 menu system compared to Drupal 8.
Providing module-defined menu links
Defining menu links in a custom module using the module.links.menu.yml file.
Providing module-defined local tasks
Local tasks are generally placed directly above content on pages(up to two levels), but can be dynamically positioned as a block.
Providing module-defined local actions
Local actions have also been moved out of the hook_menu() system in Drupal 8 and are very similar to local tasks. Use actions to define
Providing module-defined contextual links
Contextual links have also been moved out of the hook_menu() system in Drupal 8 and are very similar to local tasks.
User stories for Drupal's menu API
Adapted from [#2351379]. Here are various user stories for the menu API and how they fare against the plan at [#2407505].