SimCity 4 (lost alpha and beta builds of simulation game; 2002)
SimCity 4 is a well known city building simulator. During the development of the game, Maxis released numerous preview screenshots of the game. Some are pretty close to the end product, others show radically different graphics. None of these development versions has leaked yet. They can roughly be categorized into what appear to be early versions of the game, late versions and into marketing mockup renderings which likely never were going to be part of the game engine.
Early development versions
These screenshots show radically different graphics from the end product.
Late development versions
These look pretty similar to the released game, however there still are differences.
3D renders
These images were likely created in a 3D modelling software and not using the in-game renderer.
References
http://web.archive.org/web/20020802021915/http://www.gameport.cz/r-art.asp?id=1020408815&t=gameport
https://www.gamepressure.com/games/screenshots_list.asp?ID=1146
https://www.gamemeca.com/view.php?gid=120258
http://en.riotpixels.com/games/simcity-4/screenshots/page-6/