In the same vein of both the Best Movies NEVER Made and BEST T.V. Shows NEVER Made, I present 'Best Books NEVER Written'. Have fun.
The Age of Innocence (1920): One of the first biological works on human development during childhood, first published in 1920. The work itself paved the way from many latter studies in childhood development and human biology, but has come under increasing scrutiny in latter years because of the now infamous epilogue to the book, which focused on the positive aspects of eugenics in raising the 'perfect' child.
Anthem (1938): Written by an anonymous member of the International Brigades following the Spanish Civil War,
Anthem addresses the dangers of fascism, and overtly called for a united left flank against Italy and Germany in Europe. The book was widely popular, published first in the Soviet Union in the run-up to World War II, though it was banned for the duration of the Molotov-Ribbentrop pact. Afterward, of course, the book was put back into circulation, and circulation was increased. Famously, Stalin himself gave a copy of the work to President Roosevelt at the Tehran Conference in 1943.
The Awakening (1899): A historical work documenting the Second Great Awakening in the United States, which lasted from 1790 to 1840. Hailed by theologians and historians alike for an even handed and fair look at religious revival and schism across the United States in the early years of the republic.
Crime and Punishment (1866): An abolitionist tract pressing for radical reforms in the former Confederacy first published after the Civil War. Popular among freedmen and Northern whites, the tract itself remained in circulation until it was eventually banned by 'Redeemer' governments in the South after the end of federal occupation in 1877.
A Doll's House (1879): Muckracker work on the working conditions of maids and other servants of the well-to-do. While the work wasn't immensely popular in it's lifetime, it has been hailed as one of the quintessential works of the time period with it's open focus on Gilded Age servitude.