Twilight of the Superheroes: Alan Moore's Lost Work
Twilight of the Superheroes is classic Moore, dark, well thought out, and provides a fresh new spin on established characters. It's not his only 'lost work' out there but it's by far his most intriguing.
As I mentioned in my previous article about Alan Moore, he left DC Comics in 1989 with at least one project left unfinished: a dark crossover involving the entirety of the DC universe called Twilight of the Superheroes. It was conceived as a standalone miniseries, which would crossover into other titles at the other writers consent. Moore didn't appreciate crossovers used as a storytelling tool as it forced other books to make tentative links to the main story, or force readers to buy other comics they normally wouldn't pick just to understand the entire storyline (thankfully, these days crossovers are handled better than they used to be. Usually). Moore's idea gave writers the choice to participate in the crossover if they wanted to, by having John Constantine or Rip Hunter, two of the main characters of his proposed story, appear in the related issue, warning the characters of the book of some event. Another thing Moore wanted to achieve with the book was provide a definitive end to the DC universe. He praised Frank Miller's The Dark Knight Returns for putting a capstone on the Batman mythos, and endeavored to that with his own story. In his own words: What I'd like to do creatively with the series is to create a storyline that the whole superhero phenomenon a context that intensely mythic and from the characters involved in it their last ounce of mythic potential, the link between superheroes and the Gods of legend something as direct and resonant as the original legends themselves. One legend in particular will be the main thematic drift of the storyline: the Norse legend of Ragnarok, twilight of the Gods. Proposed in 1987, the story took place twenty years in the future (making it 2007). The world has changed. Society has collapsed, and the ordinary people have turned to the superheroes for leadership. This has caused the superheroes to form dynasties, and basically become rulers of Earth. This is all related to the present day John Constantine by his future self and Rip Hunter, who have travelled back in time to stop events that led to this dystopian future from happening. The proposal presented dark versions of the DC heroes, depicting many of them as tyrants, perverts and murderers (Superboy is portrayed as a sociopath and a sadist, Plastic man is now a gigolo), and would have been the darkest book DC had published involving their most well known characters. 
To destroy any opposition to their leadership, the hero's committed a purge of the super villain community. The villains who survived , including Lex Luthor and the Joker, formed the House of Secrets, which controls Nevada. They keep to themselves and don't rock the boat, which keeps them alive. Superman and Wonder Woman, renaming herself Superwoman, had married, forming the House of Steel with their children, Supergirl and Superboy. They control the eastern seaboard. The Marvel Family formed the House of Thunder, and control the west coast of America. They are the two most powerful houses in this future. Batman and The Shadow lead a brigade of 'normal' heroes to oppose the regime and rid the world of it's oppressive rulers. All aliens, including Green Lanterns, have been exiled from earth, forcing the Lanterns and various alien races to form a coalition to take earth for themselves, for if the heroes get bored of ruling earth where else would they set their sights but the stars. The thrust of the story would have being the proposed union of the houses of Steel and Thunder through the marriage of Superboy and Mary Marvel Jnr. This is seen as catastrophic to the the aliens and the other houses, including the House of Titans, made up of the former members of the Teen Titans, and the House of Justice, made of the former Justice League (Blue Beetle, Aquaman, The Flash etc). If they merge, they will be unstoppable and can take Earth for themselves. This leads all the remaining houses, spurred on by Constantine (who even encourages the alien's take over plan), to attack the wedding in attempt to destroy the Houses of Steel and Thunder for good. The aliens pick this time to attack also, adding to the bloodshed. Many heroes are killed, and Hunter's and Constantine's true plan is revealed: they wanted the future to come about, but made subtle changes in the past which led to the super powered heroes being destroyed, causing society to rebuild itself, under the guidance of Batman, the Shadow, and other non-powered heroes. Another thing that Moore proposed with Twilight of the Superheroes was the return of the Multiverse, gone since 1985's Crisis on Infinite Earths. This was a way of having a concrete continuity existing in the core universe, while also giving creators freedom to craft stories free from this continuity. DC would later achieve this very thing to some extent with their Else world tales, and the idea of Hyper-time, a sort of flexible continuity that allowed timelines to branch off creating alternate events that still remained canon (it proved very messy and was discontinued). 
Unsurprisingly, DC never commissioned Twilight of the Superheroes. They had done dark dystopian futures before, but never to the extremes that Moore was proposing. It basically comes across as Watchmen done with DC characters, in both style and content. When Moore left the company, the proposal stayed with them. It would probably would have never being seen by anyone, if it hadn't being leaked onto the internet in the 1990's. It's authenticity was a matter for debate for a long time before being verified by both DC and Moore to be genuine. DC threatened at least one site with legal action, claiming to hold the copyright on the proposal, an action whose legitimacy has been disputed. We will probably Twilight of the Superheroes in it's entirety, but have we seen some ideas it put forth recently? The weekly event 52 reintroduced the multiverse, and had a major plot point involving a hero working with his future self to avoid a coming disaster. Also the two examples I have already given, Else worlds and Hyper-time. I know these are flimsy arguments and can be written off as coincidences, but one argument that has being given some serious weight involves the DC miniseries Kingdom Come. Written by Mark Waid, with art by Alex Ross, it was released in 1996, and concerned a dark future where the older heroes had retired leaving the younger generation to run amok. A pastor from the present day is taken to the future by the Spectre to bare witness to the events that happen when Superman attempts to restore law and order, including the formation of several factions to oppose Superman and each other. Claims have being made that DC's efforts to suppress the proposal were because of alleged similarities between it and the miniseries. Both Waid and Ross have stated that they both have read the proposal, but any similarities are minor and unintentional. I find myself agreeing with them. It's a business built on the creativity of some very talented, imaginative people, similarities are bound to happen. But people are allowed their opinions. Twilight of the Superheroes is classic Moore, dark, well thought out, and provides a fresh new spin on established characters. It's not his only 'lost work' out there, (Big Numbers, his take on Youngblood, and Marvel pastiche 1963 all remain unfinished) but it's by far his most intriguing.