A French project to make French books published prior to 2001 and that are no longer for sale in print or online has made many books available to read online.
Following the breakdown of the Google Books Settlement court case in New York in 2011, the French Government passed a law to digitise up to 500,000 out of print books from the 20th Century.
Law No. 2012-287 makes the digitalisation of books available. The National Library of France is responsible for creating and maintaining the database and providing free access to the public. Each year a new list of titles is added.
You can see all details here: https://relire.bnf.fr/accueil