Dumbo's Flying Circus
Dumbo's Flying Circus was scheduled to be part of Atari's children's series (which included characters from Peanuts, Sesame Street, Disney, Muppets, and Garfield), but for one reason or another it never saw the light of day. Atari advertised Dumbo in European Atari catalogs and even had a prototype box made, so the decision to shelve it must have been made quite late. Even though Dumbo was developed as a children's game, the gameplay is quite difficult which may be the reason why it was never released.
The object of the game is to guide Dumbo around the screen and catch or shoot balloons before they reach the top of the screen (sort of like Kaboom in reverse). Some balloons have bombs attached to them and are deadly to the touch, so they must be shot down using peanuts from your trunk. Every now and then you will see a balloon with a clown riding it, you must shoot these balloons and catch the falling clown before he hits the bottom. If the clown makes it to the top of the screen he'll stay up there and begin to drop things on you. Every time three balloons reach the top of the screen the ceiling gets slightly lower, this gives you less and less room to grab the incoming balloons. The ceiling can be raised a bit by safely catching clowns or by winning the bonus round.
At the end of each wave you are presented with a bonus round where your mouse friend (Timothy Q. Mouse) comes flying from the left side out the screen. If you can catch him before he bounces off to the right (which is very difficult to do), you earn some bonus points and he'll raise the ceiling a bit. After the bonus round you are shown a status screen which displays the number of clowns you've caught, and the number of lives you have left.
After two waves you are presented with a strange intermission of sorts where Dumbo picks up and flies around the screen with a banner that says Dumbo. It is unknown what this intermission is for, but I've come up with two theories: Since the game was made for children this may simply be a chance for them to rest a bit before continuing on with the game, or the action on the intermission screen could correspond somehow to how your doing in the game (the better you do the more interesting the intermission).
Dumbo appears to be complete (with the exception of the intermissions), but the gameplay is still rather difficult and would need some adjusting in order to make it suitable for children. Adults on the other hand will find Dumbo to be an amusing challenge and well worth playing (just try to forget it's a Disney game).
Prototype Box Artwork (Thanks to AGH)