One of the films which had been planned to be made but were never made was Stanley Kubrick's biopic of Napoleon Bonaparte. He had done extensive work on researching Napoleon and had intended to start the film after he completed 2001 and had starting the process of casting it.
However Waterloo was released in 1970 and proved to be a financial flop. As a result the studios were not prepared to finance Napoleon.
Kubrick went on to make A Clockwork Orange instead. The closest he came to making Napoleon was his next film Barry Lyndon.
Kubrick had written to the studios saying "It's impossible to tell you what I'm going to do except to say that I expect to make the best movie ever made." It is one of those never made films which appears on lists of greatest films never made and a book was written about Kubrick's Napoleon.
Steven Spielberg has announced that rather than making a film he intends to make a television miniseries using Kubrick's screenplay. He made the film AI based on Kubrick's screenplay as his tribute to Kubrick. I hope he does a better job of Napoleon than AI as that suffered from being a hybrid of Kubrick's cold analytical writing and Spielberg's tendency towards sentimentalism.