Adaptation Overdosed

Let's say you write a book. The readers love it, the critics love it, and everyone wants to see a movie of it. But when the movie finally comes out, it's a major letdown. Or perhaps it works out fine, but a few years later, people still love the book yet don't seem to remember that the movie ever happened.

Not wanting to waste a good story, the studio makes up its mind to try again.

And again, and again, and again.

Anyway, this trope is all about stuff that doesn't merely get multiple or long-running adaptations, but actually has a whole bunch of Alternate Continuities (preferably at least three within the same medium) as a result. Perhaps in some cases, the audience will "win" and one adaptation will cement itself in the public memory for all time.... Perhaps the studios will keep playing anyway. In most cases, it seems they just can't seem to get it right, but that's always a matter of opinion.

This trope is not about works that simply have lots of sequels or vast expanded universes within the same continuity; in other words, Star Wars and Star Trek are not examples. Star Wars almost could count as an example for the sheer number of times the individual storyline of each film has been adapted. A New Hope, for example, has two Novelizations, three comic strip versions, a Radio Drama version and is retold in part of the Lego Adaptation Game. However, all but the Lego version supposedly take place in the same continuity.

Anime and Manga

 * Mahou Sensei Negima probably gets the award for the most thorough invocation of this trope in the shortest amount of time. At present, there's the original manga, two broadcast Animated Adaptations, a Live Action Adaptation, a few OVAs, a second manga released parallel to the first, a Spinoff Babies series has begun, and a movie covering an alternate end to the manga. Only the OVAs and the first manga seem to occupy the same continuity. At this rate, by the year 2020 there'll be eight or nine movies, a couple of noir or western-themed animes, and an opera.
 * Appleseed (manga, 1980s anime OVA, recent CGI movies)
 * Ghost in The Shell (manga, movies, Stand-Alone Complex anime TV series).
 * Tenchi Muyo.
 * Neon Genesis Evangelion is famous for this. The original anime and manga series are set in similar, but distinct continuities. Then after that you get into the Raising Project games, the Raising Project manga, Girlfriend of Steel/Iron Maiden, Rebuild of Evangelion, Angelic Days, Gakuen Datenroku, Eva Pucchi, the reportedly-still-under-development live-action movie... oh, and of course the End of Evangelion as possibly alternative ending.
 * Hana Yori Dango has no less than three official live action series adaptations (one in China, one in Tokyo, and one in Korea), plus a second, unofficial Chinese adaption, an anime, and the original manga.
 * Robotech spun off of Macross above, merging it with two other anime series. Then there were novelizations and RPG and comic adaptations, none of which quite perfectly matched with the others. There were spin-off novels and comics, as well. Then there was an abortive 3-episode sequel series, which was again adapted and continued three different ways in comics, novels, and game. Then there was the sequel The Shadow Chronicles.
 * The Gundam franchise. 11 main series and loads of OVA, films, manga, novels, games and plastic modeling kits, spread over 7 different continuities. There are also spin-offs like Super Deformed Gundam.
 * The Saiyan, Namek and to a lesser extent Androids/Cell arcs in Dragonball might count, as almost every game released ever since they started back in 1988 covers one or several of them and quite a few cover those and JUST those. The only exceptions are either sequels to them or the ones that cover Kid Goku-stories (Either DB or GT), which are very few. They're also the only arcs to be adapted on Dragon Ball Kai.
 * Cutie Honey (or "Cutey Honey") has four animated incarnations, two live action incarnations, and five manga incarnations. Try asking a fan of the show where Honey's powers come from. Heck, try asking them whether or not she's human; the answer changes in just about every version. You'd think they'd run out of answers to a yes/no question eventually, but no...
 * Madoka Magica. The original TV anime, a manga (plus two Spin Off manga), a novelization, a PSP game, and now a pair of Compilation Movies. And all of this was announced in less than a year after it started, so there's still the possibility of more still being created.
 * Code Geass has only one full-length anime, but there are four separate and completely different manga adaptations as well as three games based on it. As of early 2012, two spinoff OVAs, a film version of the original series, and yet another alternate-viewpoint manga are planned (the original anime came out in 2006).

Comic Books

 * Teenage Mutant Ninja Turtles also applies. Starting as a comic book series it has expanded to two cartoon series (one only loosely based on the original comics; the other a direct adaptation), two anime OVA's, two live-action specials (song themed), a live-action series, two other comic book series, a daily strip, three live-action films (number four on the way), a CGI film, several kids' books, novels, magazines, games and crossovers, and heaven know how many toys and merchandise (including a set of "automutating" TMNT transformers of all things).
 * Batman, Superman, the X-Men, Spider-Man, and indeed any comic character/organisation/series with enough fans and pages to their name have accumulated a massive number of adaptations with multiples in every medium possible, each referencing each other but clearly in their own separate continuities. It would be far easier to go to their respective pages and look at the lists there than mentioning them all here.

Literature

 * A lot of literature that is no longer copyrighted (particularly fairy tales and children's novels) gets this treatment. For example, the works of William Shakespeare, as well as most of the older stuff in the Disney Animated Canon (Peter Pan, Pinocchio, etc.). In fact, there's enough stuff in this category to deserve its own trope.
 * Sherlock Holmes definitely deserves to be mentioned separately, having been played by over 75 different actors in 211 films.
 * The Lord of the Rings has three radio dramas, a musical, a live-action film trilogy, and two animated films
 * A Christmas Carol: Has been made into no less then 19 films, including animated versions, made for tv movies, musicals, silent films, and a Muppets version.
 * I Am Legend has had three movies since it was written in the 1950s, and all of them take the plot and character.
 * Frank Herbert's Dune was almost made in the 70's. It now has a film by David Lynch (with two versions), two Sci-fi channel miniseries, a RTS game and plans for another big screen film.
 * James Bond. Novels, a largely-forgotten TV adaptation, a David Niven spoof based on the rights to the TV adaptation, one twenty-movie franchise, an Exiled From Continuity remake, and a subsequent reboot.
 * It took a TV episode and two movies for someone to get Casino Royale right, but there was also a second Thunderball (Never Say Never Again) for someone else to get wrong.
 * The Hitchhikers Guide to The Galaxy was originally a 6-expanded-to-12-episode radio comedy, then a series of novels based on it, a TV series, a sequel radio comedy series, and a movie. Each one of them considerably different from the others.
 * The Wonderful Wizard of Oz has 39 books, the classic movies and their sequels, a Muppets version, stage plays, a modernized TV series, an alternate interpretation of Oz and the villain (which in itself has a musical and an upcoming film), cartoons, anime, and a Russian translation that diverges considerably as it goes on.
 * Alice in Wonderland has 16 different film adaptations, including two by Disney, a Darker and Edgier video game, a tv show, an anime remembered in many places that aren't the States, a re-imagining book series, Sci Fi,...
 * Mutiny On the Bounty: at least three film versions, a few novels, probably a play or two.
 * Charlie and The Chocolate Factory: Two movie versions and a stage play, the last being the most faithful take. In addition there's a stage musical adaptation that incorporated songs from the 1971 movie while sticking closer to the book, video games based on the 2005 film, an opera (called "The Golden Ticket"), a ride at England's Alton Towers, and a defictionalized candy brand (originally, the '71 film was a vehicle to launch it).
 * Every decade or two, The BBC goes on a Jane Austen kick and remakes most of her most famous works (usually Pride and Prejudice, Sense and Sensibility, Persuasion, and Emma) as miniseries. Each of those four novels has three or four BBC adaptations as well as several movie adaptations.
 * And Then There Were None by Agatha Christie. They get worse and worse.
 * There have been several adaptations of most of HG Wells' books, especially The War of the Worlds and The Time Machine. The former is especially prone to getting a Setting Update about once a generation.
 * Last of the Mohicans by James Fenimore Cooper, in addition to being part of a 5-book series, has itself been adapted to film at least five times, with the last (most famous) one being a remake of a previous screenplay; a graphic adaptation by Marvel, and inspired a series of classical oil paintings when it first came out in 1827, along with having some local landmarks named after the characters.
 * Zorro has been adapted many times.
 * Phantom of the Opera, originally a novel by Gaston Leroux. Has since been adapted into goodness knows how many movies, three stage musicals (four if you count the sequel), quite a few additional novels and numerous spoofs/reworkings on TV. Not to mention a song about it by Iron Maiden.
 * Little Women has been made into several stage plays, movies, TV miniseries, anime, an opera and a Broadway musical.
 * Anna And The King Of Siam has given us one Broadway musical, four movies (two of which are based on the musical), and a short-lived sitcom.
 * The Jungle Book has had so many film and TV adaptations, both live action and animated, that Rudyard Kipling's version is probably the least well-known.
 * The Ring has been made into a film four times - twice in Japan (once as a semi-pornographic TV movie!), once in Korea (as The Ring Virus), and once in America. There have also been two Japanese TV series, three Japanese sequels, and one American sequel.
 * It was also adapted into a manga.
 * The Three Musketeers. A quick search on IM Db returned 48 results.
 * Dracula. The fact he has his own page on this very website should be proof enough of how much often he tends to appear in mediums of every shape and form. Most tend to adapt more from the famous 1931 Universal film then the original novel.

Myth and Legend

 * The King Arthur mythos, of course. Every few generations needs a new adaptation of the old stories, starting with Le Morte Darthur by Malory and moving on to Tennyson, T.H. White, Peter David...
 * Robin Hood also has a ridiculous amount of adaptations, including TV shows, movies, books, video games, and that's not even getting into "Modern Robin Hood" territory.
 * Myths in general have a LOT of adaptations, especially as different forms of the same legend. Even a myth dating from the Middle Ages will have a lot of different versions floating around.

Toys
In short: Look at this full listing of everything and try to not go too cross-eyed.
 * Transformers has to take some kind of a record. It has--let's see now--several lines of toys, the original American cartoon, several successive anime that continued from where the American one left off, five or six different comic book series spanning all the different TV show and toy eras (American and British), Beast Wars, the Japanese Beast Wars spinoffs, Beast Machines, several more Transformers anime set in Alternate Universes that were dubbed for American consumption after Hasbro succumbed to fan backlash over Beast Machines (they originally intended a sequel to that named Transformers Trans Tech), the live-action films which occupy their own AU and possess their own novel and comic adaptations, two more American cartoons which are also their own universes, and a Japanese toy and manga series called Kiss Players which involved Interspecies Romance on the Autobot side and vorarephilia on the Decepticon side.
 * And that's not even counting the Diaclone and Micro Man Japanese lines whose overstocks and remainders were sold to Hasbro to become the original Transformers toys.

Video Games

 * The Lunar JRPG series began on the Sega CD, was reworked for the Saturn and Play Station, had an updated version of the PS reworking, another GBA remake, and is now being remade a fifth time. The Play Station version is generally best-known (and sadly rather thicker in cliches than the Sega CD original).
 * Super Mario Bros. Less so now, but as well as the games there are the spinoff games in about ten series, three cartoon shows, about four anime films, the live action film, various manga series, three series of American comic books, German comics in Club Nintendo, the Ice Capades, books, and random series that have very little to do with anything (Mario All Stars cartoon series consisting of recycled stuff from the first three, King Koopa's Kool Kartoons...)
 * Sonic the Hedgehog has an anime, an adaptation of that anime, an OVA, two American animated series that were launched simultaneously, a US comic, a UK comic, several Manga, and numerous 90s book adaptations not based off any comic. And we haven't even mentioned the games.
 * Pokémon: There's the original games, the spin-off games, the remakes of the older games (which both expand upon the originals and retcon certain aspects of them too), the anime, the manga adaptation of the anime, various adaptations of the games, over 30 other manga which seem to do their own thing separate of other continuities... And that's just the beginning.

Western Animation

 * Scooby Doo spawned numerous Animated Series, including a Spinoff Babies series, as well as many animated movies ("Reluctant Werewolf" and "The Ghoul School"), several live action movies, more animated movies ("Zombie Island", "The Alien Invasion", etc.), another animated series with a modern update, and many more animated movies based off of that series.