“125,000+ free books” is the sort of number that deserves an explanation. Here is exactly where it comes from, and why none of it is piracy.
That is the whole trick. Copyright is a fixed-length monopoly, not a permanent one. When it expires, a work enters the public domain and anyone may copy it, print it, record it or sell it. No licence, no fee, no permission.
The exact term depends on the country and on when the work was published, which is why a book can be free in one place and still protected in another. What it means in practice is that essentially the entire literary canon written before the 1930s is now free for anyone to use.
Started in 1971, and the oldest digital library there is. Volunteers proofread scanned books and publish clean, well-formatted text. The catalogue is past 79,000 titles and every one of them has been checked to be in the public domain in the United States before it goes up.
This is where the text comes from when Aloud reads a classic to you.
The same idea, but out loud. Volunteers record public domain books chapter by chapter and release the recordings into the public domain too. Over 20,000 works read by real human beings, free to download and free to keep.
These are genuine human recordings, not synthesis. Quality varies with the reader, which is part of the charm and occasionally part of the problem.
A catalogue rather than a source: an open, editable index of books run by the Internet Archive. It is what makes the number reach six figures, because it catalogues public domain editions that Gutenberg has not got to yet.
It puts all three in one search box, and then does the part none of them do: if a book has no human recording, your iPhone generates one. The narration is synthesised on the phone itself, so it works on a plane, it does not use a server, and there is no limit on how much you listen to.
Aloud only pulls from catalogues that guarantee public domain status at the source. There are much larger archives on the internet with much messier rights, and they are deliberately not wired in. A free audiobook is only worth having if it is actually legal.