Current status: very much a work in progress. Branches are being developed simultaneously for Drupal 7 and 8. For further details, see the waffle.io board.
Background: As of 2012, an estimated 24 percent of U.S. government websites (including whitehouse.gov, most famously) were Drupal sites. That number has only continued to increase.
Just as the Bootstrap theme bridges the gap between Drupal and the Bootstrap Framework, a USWDS theme will make it simpler and easier for Drupal site administrators to use the U.S. Web Design Standards. A Drupal 8 version of the theme will additionally make it easier for site administrators to update to this major new version of Drupal.
Further context: uswds/uswds#852
This project is in the worldwide public domain. As stated in CONTRIBUTING:
This project is in the public domain within the United States, and copyright and related rights in the work worldwide are waived through the CC0 1.0 Universal public domain dedication.
All contributions to this project will be released under the CC0 dedication. By submitting a pull request, you are agreeing to comply with this waiver of copyright interest.