There's probably hundreds of Disney films considered for animation in some form or another that never made it. At least, several dozen have come to light.
These films were all considered in various capacities - from Disney simply buying the rights, to an official pitch, to actual pre-production (songs made, script written, or character sketches).
Here is just a sample of Disney Animated Features that were not realized, there are plenty more than this:
"Abarat" - based on the Clive Barker book was seriously considered before Barker became wary of selling Disney the copyrights to his story.
"Wild Life" - was a 2D film about animals who sang in a night club.
"Fraidy Cat" - was a CGI film about a cat and parrot in a Hitcockian comedy/thriller.
"Don Quixote" - was an adaptation of the classic story by the Brizzi Brothers.
"My Peoples" - these doll-like inventions of spare parts come to life and help two people in Appalachia - a love story. It was going to be 2D figures against a CGI background, I believe.
"Ramayana" is supposedly coming back as a 2D project.
"Fantasia 2006" was an idea of Roy Disney - 4 segments were completed: John Henry, Lorenzo, The Little Matchgirl, One by One - 3 of the 4 are now on DVD.
"The Search for Mickey Mouse" - the original 50th Disney film, it was going to see Mickey kidnapped and Minnie hires Basil of "The Great Mouse Detective" to find him, many classic Disney characters such as Alice and the Dwarfs would have had cameos - it was scrapped when it became too hard to figure out why all these character's worlds would be collided.
"Aida" was canceled and made into the stage musical, instead.
"Chanticleer" was canceled in part thanks to Don Bluth doing it first with "Rock-a-Doodle".
"Cuban Carnival" - would have made Saludos Amigos/The Three Caballeros a trilogy, except it was canceled when the previous two did not gross what was expected.
"Gremlin Lore" - the story by Roald Dahl was considered as a full-length wartime feature rather than the hybrid "Victory Through Air Power."
"The Hound of Florence" - a possibility in the 40's - a human becomes a dog who solves crime.
"Scruffy" - This wartime tale told of Scruffy, one of the famous apes that live on the Rock of Gibraltar. In the Disney version, there would be a villainous Nazi spy to be outwitted, and a beautiful she-ape to be wooed.
"Babar" - Disney owned the book rights and had considered an animated film.
"Hiawatha" - An animated version of Longfellow's famous poem Hiawatha was planned as far back as 1948. Beautiful characters were designed, like Kabibonokka, the spirit of the North Wind. Although the story was never fully developed, much of the style of the movie was resurrected when Disney animators used it as a style blueprint during the production of Pocahontas.
"Hansel and Gretel" - would have starred Mickey and Minnie in the titular roles, the Sherman brothers even wrote songs for it.
"The Four Musicians of Bremen" was in preparation around 1969. Walt had already explored this Brothers Grimm tale in a 1922 Laugh-O-Gram 7 minute silent movie, but after his death the company thought of remaking it in long form with a then-contemporary setting. The musicians were to be played by unloved animals who try to educate the town in the virtues of Beatle-esque rock music. Unlike some of the other ideas here, this one looks pretty weak; it's one of many examples of how the company was unsure of itself in the period following its founder's passing.
"Uncle Stiltzkin" - a parody twist on the tale of "Rumplestiltskin". Disney had a script written for it.
"Sinbad" - Disney had a script written by "Treasure Planet" and PotC writers Ted Elliott and Terry Russio.
"John Carter of Mars" - before becoming a Pixar flick, it was pitched in both the 30's and 80's to be a Disney animated film.
"Where the Wild Things Are" - was used to do a CGI test footage by John Lasseter in the hope it may become a new Disney feature.
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Also consider films that were changed/made elsewhere:
"The Wild" - one reason it could be considered canon is because it was not fully an outside project that Disney only distributed. It was all planned inside Disney, first as a live-action project, than as an animated project - and eventually was given to C.O.R.E. to make once it was planned inside Disney.
"Rapunzel Unbraided" - originally "Rapunzel" was going to be a parody of fairy-tales like "Shrek" or "Enchanted."
"American Dog" - "BOLT" was originally going to be more quirky, with a dog who battles gangsters at Casinos with help from a cat with an eyepatch and a giant, radioactive rabbit.
"The Prince of Egypt" - a Disney animator swears he pitched the idea to Jeffrey Katzenberg who turned it down before leaving Disney for DreamWorks, where the film was never heard from again...
"Kingdom of the Sun" - originally, "The Emperor's New Groove" was a new take on "The Prince and the Pauper" by Roger Allers, where Yzma was scary and had a voodoo magical wooden staff. It became too serious and too long in production so it was scrapped and became a comedy. ("The Sweatbox" is a documentary Sting's wife made about it, and Disney has refused to let the film be released as it portrays their animation process negatively.)
"The Little Mermaid" was originally planned by Walt himself, but in a much darker version of the story.
"The Brave Little Toaster" - John Lasseter pitched this to Disney as their first CGI film all the way back in the 80's but was fired for even thinking CGI could be a medium in film.
Also, many films were downsized into shorts when they weren't meaty enough for full-length features.