Collecting and sharing public domain works on sites like Project Gutenberg was one of the earliest uses of the internet. Today collections of public domain works have proliferated to such an extent that a definitive list would be extremely difficult for one person to compile (and maintain) in one place.
Luckily, the dedicated volunteers at Wikipedia have taken a keen interest in this subject and their Wikipedia:Public domain resources page collects and updates links to dozens of sources of public domain material across a wide range of subject areas. Public domain images are sufficiently popular and useful that they get their own page. The entry on the Public Domain in the United States lists exemplary works of literature, music, and other genres. Finally, public domain films get their own exhaustive list.
In addition to the Wikipedia pages, three sources of public domain texts bear mention because of their size and scope:
- The HathiTrust Digital Library (HDL) is a collection of millions of digitized texts contributed by research libraries, including the UVA Library, and it provides full-text downloads of books determined to be in the public domain.
- Google Books also contains millions of digitized books. It was first developed in partnership with research libraries, and the books digitized in that partnership were deposited in the HDL as well as in Google’s search corpus. Public domain works are usually downloadable in full text from Google Books. While Google Books and the HDL started from the same digitization effort, thay have grown independently since then, so it’s worth searching both collections.
- The Internet Archive is a collection of publicly accessible texts and other media from a wide variety of contexts. Not all of its collections are in the public domain, but a substantial portion is.
Finally, while it is not a collection of the works themselves, this spreadsheet from Duke’s Center for the Study of the Public Domain will be helpful if you’re interested in identifying works from 1923 that entered the public domain in 2019.