The Public Domain Review is an online journal and not-for-profit project dedicated to the exploration of curious and compelling works from the history of art, literature, and ideas. Check out PDR's free to download colouring books, Zoom backgrounds, and Collections (including these beautiful illustrations from Japanese fireworks catalogues).
The Center for the Study of the Public at Duke Law School promotes research and scholarship on contributions of the public domain. See Public Domain Day 2022 for works that entered the U.S. public domain this year.