After Isaac Asimov's death, Greg Bear, Gregory Benford and David Brin each wrote a novel for a new Foundation trilogy. The novels take place after Prelude to Foundation, while Hari Seldon is developing his psychohistory into a full-fledged tool for predicting the future. At times, the books are surprisingly good, especially Brin's concluding novel. I think they are better than Foundation and Earth or Prelude to Foundation (I haven't read Forward the Foundation). For example, Brin dissects the concepts of ideology and morality by introducing competing factions of robots with different ideas of how to interpret the Three Laws of Robotics. Not all robots accept the Zero Law. Unfortunately, I think there are also many lows in the books, like long stretches of filler, and far-fetched plot twists.
