There were two versions of Fallout 3 that never released

Prior to Fallout 3 releasing, Obsidian Entertainment (known as Black Isle Studios back then) had worked on two versions of the game, one the widely known Van Buren project and the other a game set in a 3D world. While the Van Buren project got canceled, the other 3D project went on to become Icewind Dale.

With the 3D project, the developers were looking to take a 2D engine, which Fallout had been using, and take it to the next level – at least according to the CEO of Obsidian Entertainment, Fergus Urquhart, in an interview with IGN:

“Now 3D was the cool stuff. So we were going to move from being a 2D engine and be a 3D engine, and so we actually started working with this 3D technology called NDL."

Apparently, this game's development hit issues because the game publisher behind it couldn't give it enough funding – they publisher had hit some financial issues. Because of these issues, the 3D game became Icewind Dale instead of Fallout 3.

We will never know what would have become of the game the became Icewind Dale, but the 3D technology called NDL that was being used to power it was eventually used for Fallout 3.