The Neandertal Parallax
I remember some interest in Neanderthals on this forum.
I just read a science fiction book, "Hominids", by Robert J. Sawyer. The book is the first of a series. It deals with Earth scientists from two alternate Earths. One is our world. The other is a parallel world where Neanderthals are the species that survived. They achieve contact when things happen to experiments. They attained "heights of culture and science comparable to our own, but with a different history, society, and philosophy"
I thought it was a good read and am starting the second book of the series now.
I recommend it.