Free. Everyone gets this.
Listen reads your book aloud, one sentence at a time. The sentence being read is underlined, and the page turns by itself as the voice moves on. It works for EPUB and PDF books.
Free Listen uses the voices already on your computer. On a Mac, these are the voices in System Settings, under Accessibility, Spoken Content. For natural-sounding voices that work offline, see Natural offline voices (Pro).

If you don’t see the listening bar, press the headphones button in the Reader toolbar.
It sits under the book’s title, in the same place for everyone. With Pro nothing moves: the PRO badges go away and those buttons start working.
Free listening stops at the end of each chapter; press Play to start the next one. PDFs follow the same rule: a PDF with its own chapters (a contents list inside the PDF) stops at the end of each chapter, and a PDF without chapters stops after every 10 pages. The bar always says where it will stop. With Pro, listening can keep going to the end of the book.
While the voice is playing, click any sentence on the page and it reads from there. This works in EPUB books.
Reading Vault remembers where the voice stopped. Next time you press Play in that book, it carries on from there and tells you so.
Listen reads across page breaks and turns the page as it goes. It skips page numbers and the headers and footers that repeat on every page.
In Settings, under Read aloud, pick your reading language and tick the voices you want under Voices to choose from. Press ▶ to hear a sample first. Only natural-sounding computer voices are ticked to begin with; Show all Mac voices shows the novelty ones too. See Settings and folders.