I just finished Fleet of Worlds by Larry Niven and Edward M. Lerner, a prequel to Niven's Ringworld.

Fleet of World is an OK book but nowhere near as good as Niven's earlier Known Space books, including Ringworld. The new book adds to the backstory of the Puppeteer's homeworlds, which are seen in Ringworld fleeing an explosion at the galactic core. It also adds adds to the Puppeteer's interactions with humans by adding a group of humans that accidentally discovered the Puppeteer's home and were enslaved for generations.

Books like this are tricky as the author is either over-constrained by the previous novels or changes things in such a way that it can diminish the original novel. Fleet of Worlds fits in the second camp. Some of the things that happen in this book make the events of Ringworld seem less meaningful.