Not sure if it quite fits but Duke Nukem Forever's 2001 iteration. The developers were pursuing the latest technology and found themselves having to re-do large chunks of the game to accommodate a new Doom 3 style renderer as everything had been built around static lighting up until 2003. Apparently by the end of 2002 it was largely playable before they were stuck in a cycle of recreating textures and redesigning chunks of the game, and eventually being left to play catch up for the next several years. Unfortunately despite a dozen leaks of gameplay clips and screenshots Randy Pitchford, who owns Duke Nukem and has a license from Take-Two to re-release Duke Forever and anything related to it, insists there is no game and it's a pile of random content that doesn't function, whereas former 3D Realms developer Charlie Wiederhold (Worked on Duke Forever 1998 - 2006) has said by the end of 2001 every part of the game was represented and all the levels were linked together and there's loads of content. Frederik Schreiber, VP of 3D Realms similarly claims at the end of 2002 roughly 90% of the content was represented with only the last 'zone' (Area 51) not being complete at that stage.
Basically, there's a build of Duke Nukem Forever from the end of 2002 that is for all intensive purposes a largely playable version of what was in the 2001 trailer but legendary camgirl enthusiast Randy Pitchford won't allow it to be released and, despite leaked footage and screenshots as well as accounts from developers and other people who have this content to the contrary, claims nothing exists.