anonymous
This particular site does allow it to a very limited extent, namely 10 per domain per year.

http://www.thefreelibrary.com/_/publishe...

This actually the one I had originally in mind due to its set of APIs related to bibliographic data but it seems focused more on providing reading material in general rather than doing so exclusively online.

http://openlibrary.org/developers
posted by [UserVoice eli] • 5 years and 3 months ago Link