Classical Music: The Era of Haydn, Mozart, and Beethoven: Norton Introduction to Music History, by Philip G. Downs (1992), presents a useful study of Mozart and his contemporaries.
Shaffer's play Equus, produced in 1973, presents another exploration of two men of widely differing personalities linked by a common spiritual bond.
In Mozart in Revolt: Strategies of Resistance, Mischief and Deception (1999), David P. Schroeder examines the letters Mozart and his father wrote to each other. He discovers important information about the personality of each man as well as their relationship to each other.
1791: Mozart's Last Year, written by H. C. Robbins Landon and M. C. Landon (1999), explores the controversial last year of Mozart's life and the rumors of Salieri's involvement in his death.
Jean-Paul Sartre's play Nausea (1938) deals with existential themes as Amadeus does. In Sartre's play, the main characters must cope with a God-abandoned universe and turn to art in an effort to alleviate their sense of meaninglessness.