The Harvard Library
The publisher P F Collier and Son over 100 years ago asked the president of Harvard to build a list of books he recommended to provide an overview of Western civilization. His list was 50 volumes - some of which are one book; others are two or three works. It is known as Prof Eliot's 5-foot bookshelf of 1910. Later Prof Eliot also did a series of fiction - seventeen volumes. (Though the original list contains some fiction.)
In print: they sold thousands of copies. Used sets are always available at Ebay.
Online - Prof Eliot’s five-foot library at Open Cultures is the overview. They lead to the following four online sources for the full set.
Eliott's FULL texts, the scanned originals are at Archive.org
Internet Archive is actually at archive.org. It has the full set in plain text, Epub, Kindle, PDF for download and html (for online reading)… and some I am not familiar with.
At Project Gutenberg. They have four formats: plain text, Epub, Kindle for download and html (for online)
And Bartleby has the full set in html for online reading:
I learned about this in Weekly Standard magazine.