The Wall by Marlen Haushofer; Children of God and the Sparrow by Mary Doria Russell and Doris Lessing's 5 part series, Canopus in Argos, which began with Shikasta all come to mind.
I read Shikasta when it was first available in 1979. Now so many years later, much of the story remains alive in my memory. The four other books in the series did not capture my attention as much, and as the series went on, it got more and more diffuse and dense. But the Doris Lessing who won a Nobel Prize is evident in nearly every page of Shikasta and in some unexplainable way is related to the last of her Children of Violence series, The Four Gated City- an escape North to an unnamed place of sanctuary.
Haushofer's book was hard to find, but I did with the help of a book dealer friend. It appears to be more accessible these days, yet it was only four years ago that I read it as part of an online book club. A German friend and group member recommended it, and we later compared the Wall to Cormac McCarthy's The Road as two uniquely original dystopias. Haushofer's is a cliff hanger.
Russell's series was riveting when I read it in Vermont during my long sojourn just over four-and a half years ago. It was recommended by my closest friend, and a person I share many books with now and over the nearly 40 years of our friendship. I learned just last week that there is a third in the series, and I'll have to catch up with the conclusion. The story is both religious and inventive. A quick read, and exceptionally well drawn.