A World Out of Time

This was one of the first Niven novels I ever read, and it was quirkily wonderful. It wasn't set in "Known Space", but it did use well-established Niven technology - Bussard ramjets and suspended animation - to allow relativistic time travel from and back to, a changed Earth.

I still remember this book vividly: cats like snake-scarfs, witch-like ancient women, a HOT Earth - and a smart AI that could move planets. What's not to like? Still a favourite!