Super Paper Mario (unreleased GameCube version of RPG; 2006)
The beta version of Super Paper Mario's title screen as is still in the Wii version's files, was the title screen for the GameCube version
Super Paper Mario is a video game for the Nintendo Wii system, released in April of 2007 in North America. However, the game was originally going to be released for the Nintendo GameCube, and a GameCube build of the game was shown at E3 2006, seemingly near complete with a planned 2006 release date. Due to the release of the Nintendo Wii and discontinuation of the GameCube, the game was reworked for the Wii and delayed to April of 2007. The GameCube version of the game as shown at E3 has not resurfaced since.
The game was originally a GameCube exclusive and was at one point considered for release on both the GameCube and the Wii. Ultimately, it was made a Wii exclusive, leaving the GameCube version lost.  Some articles from around E3 2006 mention various differences that the GameCube beta had, such as character names and how various features of the game would be activated differently. There is an N-Sider article from this period of time written by someone who played the GameCube build before release, said article featuring several differences from the final version. 
A copy of the GameCube build has not been leaked in any form, and as such, this version is currently lost.
- "MarioWiki page on beta elements of the game which mentions the GameCube version":http://www.mariowiki.com/List_of_Super_Paper_Mario_pre-release_and_unused_content
- "N-Sider article":http://www.n-sider.com/contentview.php?contentid=349