Pathauto

The Pathauto module automatically generates URL/path aliases for various kinds of content (nodes, taxonomy terms, users) without requiring the user to manually specify the path alias. This allows you to have URL aliases like /category/my-node-title instead of /node/123. The aliases are based upon a "pattern" system that uses tokens which the administrator can change.

Drupal 8+ Requirements

Token
~~CTools~~, removed in 8.x-1.11, still required in composer.json for BC reasons, see release notes for more information.

Drupal 7 Requirements

Token

Known issues

D7: Multilingual URL alias support is still a little unstable and should be tested before used in production. See this issue in core #269877: path_set_alias() doesn't account for same alias in different languages which is very important and needs more coders/testers/reviewers. There is also a list of issues related to i18n in Pathauto which needs someone to help triage, test, review, and write fixes.

Recommended modules

Redirect (D7, D8) when installed Pathauto will provide a new "Update Action" in case your URLs change. This is the recommended update action and is considered the best practice for SEO and usability.
Global Redirect (D7) ensures that your content is only visiable at the one, best URL possible (i.e. requests for node/2 are forwarded to "alias-for-node-2"). This is part of Redirect in D8.
Pathologic (untested, but may help with updating outdated links in existing content)
Sub-pathauto (D7) provides a way to use one alias for multiple URLs as long as the so that "node/1" is aliased to "about-my-site" then you can use "about-my-site/edit" to access "node/1/edit". Neat!
Transliteration (D7) is useful if your site is likely contain characters beyond ASCII 128 and you want them transliterated into ASCII 128. In Drupal 8, Pathauto uses the API provided by Drupal core.