The Second Foundation Trilogy was authorized by Issac Asimov's family after his death. Its three authors centered it around Hari Seldon and set it between parts of Forward the Foundation and Foundation novels, making it a midquel to them.
1. Foundation's Fear, written by Gregory Benford in 1997
Hari Seldon is working on a project to ease the inevitable collapse of the universe-spanning Empire and the Dark Ages that will ensue. But the current emperor has other plans, like appointing Seldon first minister and thus thrusting him into a world of political intrigues and assassination attempts that ultimately will bring him up against future history's greatest threat.
2. Foundation and Chaos, written by Greg Bear in 1998
With Hari Seldon on trial for treason, the Galactic Empire's long-anticipated migration to Star's End is about to begin. But the mission's brilliant robot leader, R. Daneel Olivaw, has discovered a potential enemy far deadlier--and closer--than he ever imagined. One of his own kind. A freak accident erases the basic commandments in humaniform robot Lodovik Trema's positronic brain. Now Lodovik's service to humankind is no longer bound by destiny, but by will. To ensure his loyalty, Daneel has Lodovik secretly reprogrammed. But can he be trusted? Now, other robots are beginning to question their mission--and Daneel's strategy. And stirrings of rebellion, too, are infecting their human counterparts. Among them is a young woman with awesome psychic abilities, a reluctant leader with the power to join man and robot in a quest for common freedom, or mutual destruction.
3. Foundation's Triumph, written by David Brin in 1999
Hari Seldon escapes house arrest on Trantor to investigate what is sowing chaos in the galaxy so quickly that it threatens the downfall of civilization. Rebels from the "chaos worlds" oppose him, robots, and the empire, and R. Daneel Olivaw, the Immortal Servant, is trying to prevent a civil war between the Giskardian robots, who are willing to harm individual humans in the long-term interests of all humanity, and the Calvinians, who remain loyal to the famous old three laws of robotics. R. Daneel and Seldon finally meet on a ravaged, primitive Earth, which recalls Asimov's charming Pebble in the Sky, and agree that the robots likely will evolve into an independent race while protecting humans from their own weaknesses. This literate, intelligent coda to a grand vision of human evolution will be appreciated even by those who think four of sf's most powerful talents have spent too much time making Asimov's universe coherent.