Riverworld

Dayworld leads a sf trilogy by Philip José Farmer set in a dystopian future in which an overpopulated world allocates people only one day a week. The other six days they're in suspended animation. The focus is on Jeff Caird, a daybreaker living more than a day a week. He's not like most daybreakers. He belongs to the radical Immer group working to create a better government. Not all Immers are daybreakers, but send information from one day to the next they've daybreakers like Jeff. Immer daybreakers assume seven different personalities & jobs, slipping from culture to culture in seven different worlds. While Jeff & the other six go day to day, they run into problems while working as Immer daybreakers. They must cover their tracks while trying to keep up with seven different lives, families & jobs. It could drive a man crazy. It does & the Immers must dispose of Jeff to keep the rest safe. Jeff, wanting to live, tries to escape, but they have undercover Immers in every job & government level. Jeff is caught & put in an asylum, classified with multiple personality disorder. If considered incurable he'll be killed. But Jeff has an escape plan.
The sequels are Dayworld Rebel, '87 & Dayworld Breakup, '90.

When Robert Wolff found a strange horn in an empty house, he held the key to a different universe. To blow that horn would open up a door through space-time and permit entry to a cosmos whose dimensions and laws were not those our starry galaxy knows.

For that other universe was a place of tiers, world upon world piled upon each other like the landings of a sky-piercing mountain. The one to blow that horn would ascend those steps, from creation to creation, until he would come face to face with the being whose brain-child it was.

But what if that maker of universes was a madman? Or an imposter? Or a super-criminal hiding from the wrath of his own superiors?

The Maker of Universes is unlike any science-fiction novel you have ever read, it is wonderfully unique.