What book has sold more copies than any other after the Bible?

The Little Red Book (Mao Tse-Tung)

No-one really knows - the Bible is out of copyright, and is (and has been) distributed in a huge number of editions, most of which we have no information about.

It is speculated - but unproveable - that the three biggest-selling books of all time are the Bible, the Koran and the Thoughts of Chairman Mao... but not necessarily in that order.

It is similarly speculated that the best-selling novel of all time is Don Quixote.

"Gigapie's Big Book of Love Poetry and Kindly Remarks," by Ursula Hirohito Gigapie III. It's a big seller because it's zero pages long and costs only one cent.

Pilgrim's Progress does indeed come up on one list, but not this one: https://en.wikipedia.org/wiki/List_of_best-selling...

I'm not inclined to spend the time chasing down why that is.

It's Pilgrims Progress by John Bunyan.

The second most widely read book after the Bible is the Quran with an estimate of about 3 billion copies in print. The most read non-religious book is "The Quotations of Chairman Mao" of which there are estimated to be at least 800,000,000 printed copies. The most printed novel is "Don Quixote" by Miguel Cervantes.

I believe it is the Guinness book of World Records

Perhaps "The Little Prince."