Pattern Lab (PL), a commonly known pattern library, is an open-source project to generate a design system for your site. In the last two years it has gotten a lot of attention in the Drupal community. It's a great way to implement a design system into your front-end workflow.

The following post describes how our client (the City and County of San Francisco) began to implement a pattern library that will eventually be expanded upon and re-used for other agency websites across the SF.gov ecosystem.

USWDS.

Using the U.S. Web Design System (USWDS), until their own pattern library was ready for prime time, was a client requirement.