Not a book but a movie (and, coming from me, it’s somewhat naturally a martial arts movie). Jet Li’s HERO is told from different points of view – though a major critic at the pre-screening didn’t seem to understand that when he was doing his write-up. I found it rather Rashomon-ish, but not difficult to follow. It’s a very long movie, though.
I dunno if there’s a book preceding or derived from the movie. It was his penultimate epic movie. (He didn’t drop out; he just decided not to do more epic/historical stuff any more.)
The first one that came to mind is Patrick White’s The Solid Mandala - it switches back and forth between two brothers’ viewpoints. It’s not first-person, if I remember right, but it does get inside their heads.
Wonder, by R. J. Palacio. It’s a YA novel, but a great read for adults as well.
Looking up the Amazon link made me discover that an additional chapter – The Julian Chapter – was published earlier this year, from the POV of a character we meet but don’t hear from in Wonder. Apparently it’s only available as either an ebook or an audiobook. I’ll be reading it on my Kindle after work today.
I read Piers Anthony’s, Incarnations of Immortality series, a couple of decades ago or so. It’s the same story line told from at least 6 different characters points of view. It was fun then. Not sure what I’d think of it now.