Banjo-Threeie (cancelled sequel to platformer game series; early 2000s)
Banjo-Threeie is a cancelled video game that was developed by a British video game developer Rare and was initially going to be published by Nintendo, and later Microsoft Studios (Microsoft Game Studios at the time). The game was going to be the third installment in the Banjo-Kazooie franchise. It was initially developed for the Nintendo GameCube, and later due to Microsoft's purchase of Rare , Xbox and Xbox 360. It is rumored that parts of Banjo-Threeie are present in Banjo-Kazooie: Grunty's Revenge for the Game Boy Advance.
Teaser in Banjo-Tooie
At the end of Banjo-Tooie, Gruntilda Winkybunion (the franchise's antagonist) hints of Banjo-Threeie, telling the player she will be back in that game. 
Spaceworld 2000 Tech Demo
In Spaceworld 2000, a video game event, a few tech demos for the Nintendo GameCube were shown. Games such as Luigi's Mansion, The Legend of Zelda: Twilight Princess and Super Smash Bros. Melee were shown there. A tech demo titled Banjo-Threeie was also shown . It is speculated that after Gruntilda was defeated in Banjo-Tooie, her henchmen would try to get revenge against Banjo and Kazooie. In the tech demo, Banjo and Kazooie are pursued by a horde of enemies, which could mean that the speculation was the initial plot of Banjo-Threeie(the page is in Spanish, so use Google Translate).
Microsoft's Purchase of Rare
Because game development costs gradually increased and Nintendo didn't give more money to Rare for game development, Rare looked for potential buyers. In early 2000, workers from Activision and Microsoft started to visit Rare with purchase offers. Originally Activision purchased Rare, but Microsoft ended up increasing its offer at the last minute. Then on September 24th 2002, at a Microsoft X02 Europe event, Microsoft announced that they have purchased Rare Ltd for $375 million.
Banjo-XAfter Microsoft's purchase of Rare, a build titled Banjo-X was found on an abandoned Xbox development kit, which was dated June 2004. Unfortunately, while attempting to boot the code, a black screen would show with white text that says that some files are missing. , Mr. Termite and Mumbo were shared on Twitter by 2 of the game's developers. In one of the tweets, a fan asked if Banjo-X was a remake of Banjo-Kazooie with a co-op mode or if it was third chronologically, and Steve Mayles (one of the game's developers) responded by saying 'I remember 4 Banjos running around, but not much work was done on design, I don't think. Or levels.' He also confirmed that the art style that was used in Banjo-Kazooie: Nuts and Bolts was settled on in early development and that Banjo-X was in development in 2005. In a different tweet, Ed Bryan (another developer of the game) confirmed that in the Mumbo animation, Mumbo said 'Come and have a go if you think you're hard enough', and that it was a new model made to see if lip syncing was possible with the mumbling speech used in the Banjo-Kazooie franchise. He also confirmed that the animation was made circa 2004. It is rumored that the game would've broken the fourth wall and the all characters would gradually become aware that the game was a remake/remaster of the original Nintendo 64 version, which could have lead to interesting events. Steve Malpass (another developer of Banjo-X) stated 'All the puzzles and tasks in that level--we would see how we could adapt them. Conga the Ape, for instance, would realise he had fought Banjo and Kazooie on Nintendo 64 and act differently'. Items from Banjo-Tooie in the game would also be a possibility. If this was the case, there is a possibility that Banjo X was Banjo-Threeie. Later in development, the developers thought that the game wouldn't sell because fans would have wanted a new Banjo-Kazooie game, and not a remake, so the development team decided to mix Banjo-X and Banjo-Kazoomie (which was a prototype for Banjo-Kazooie: Nuts and Bolts). In the game, the player would have had constant access to vehicles and vehicle construction. The team still wanted the game to stay similar to the previous 2 games. Microsoft decided to focus on the vehicle access because it was a unique concept to be added to a puzzle game. Because of that the game turned into Banjo-Kazooie: Nuts & Bolts.
In 2006, a trailer for the game was released. in it, Banjo and Kazooie (the franchise's protagonists) found a door, opened it and found a world full of Jiggys, Music Notes and Honey Comb Pieces (the franchise's collectible items). They run around the world, crash into a wall, and the trailer ends.