A few of the glorious Little Blue Books, published by socialist newspaper editor Emanuel Haldeman-Julius. Starting in 1919, Haldeman-Julius began printing cheap, pocket-sized booklets intended to make discussions of literature, science, sexuality, politics (and, apparently, ventriloquism) accessible to The Masses. The Little Blue Books would remain highly popular throughout the twenties, thirties, and early forties, until, following World War II, their treatment of socialism, homosexuality, and atheism earned them a blacklisting from the FBI. By the time Haldeman-Julius died in 1951, the series had virtually been forgotten.
A wide range of titles (without PDFs, sadly) is available for perusal here, including such attention-grabbers as: "The Socialism of Jesus", “How to Win Prize Contests”, “Homosexuality in the Lives of the Great”, “The Marvels and Oddities of Sunlight”, “War, What For?”, and “Various Types of Venereal Diseases and their Treatment”.