HathiTrust has a mission to ensure the long-term preservation and accessibility of materials in the digital archive. You can search HathiTrust for books that are in the public domanin.
The Directory of Corporate Archives includes institutions that maintain their historical records themselves, as well as companies that contract with historical consulting firms to maintain their archives collections for them. This edition also includes the archives of professional associations, as these collections document various industries and companies that may be of use to corporate archivists.
In their own description "HathiTrust is a partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world."* Partner libraries share digitized content with other members of HathiTrust and public domain content is open for everyone. Some content is restricted to particular institutions.
The Internet Archive is a non-profit that archives Internet sites, multimedia, and texts in digital form. Much like a physical library, it provides free access to researchers, historians, scholars, and the general public. Many University contribute with their collection digital or print collections to the Internet Archive.
* see, https://www.hathitrust.org/