The Alterra Project Windows game

Imagine an RPG game world that functions during the day as you'd expect it, with NPCs roaming around, interacting with the player and other things around them, and going about daily activities on a timed schedule. But after the sun sets, a new world surfaces. One very similar to the other but different in structure, dark where there once was light and vice versa, not only is the world affected but every character in the game but the player is affected as well, giving every character a second personality that operates during the night for better or for worse.