The Archive of Alternate Endings by Lindsey Drager is my absolute favorite.

honorable mentions:

• Slumberland by Pauly Beatty
• A Confederacy of Dunces by John Kennedy Toole Slaughterhouse-Five by Kurt Vonnegut Kafka on the Shore by Haruki Murakami The Thought Gang by Tibor Fischer The Things They Carried by Tim O’Brien The Cider House Rules by John Irving-