4 3 2 1

4 3 2 1 by Paul Auster, 866 pages.
This extraordinary novel opens with a joke a that tells how the main character's grandfather, Isaac Reznikoff became Ichabod Ferguson. The joke is repeated near the end of the book, and this framing, and it's accompanying explanation somehow tie together the four different lives of Archie Ferguson. The novel presents four different lives for Archie, four different paths that his life could take based on different decisions made when Archie was still young. Each chapter has four versions, 1.1, 1.2, 1.3, 1.4, then 2.1, etc. (chapter 1 actually has a 1.0, too, before the split)
A phenomenal book, really one of my all-time favorites. Strongly recommended for fans of Kate Atkinson's Life after Life (and, of course, A God in Ruins), David Mitchell's The Cloud Atlas, and other literary works with a speculative edge.