Uldrus: Ice and Darkness
The people of Uldrus had grown accustomed to constant, unrelenting sunlight. They had never known the cool and quiet of the night; the deathless day had always been. But they had adapted to these conditions over the course of generations. Their crops flourished and their cities grew. They gloried in the blessings of Luxis, the goddess of light and life and love. While the world was not free from such strife as will arise between neighbors or between nations, there was general prosperity and calm. Seldom did anyone ever look to the western horizon, where the blue of the sky began to deepen and darken into black, to wonder what lay beyond the borders of the sunlit realms.
Until, all at once, the inhabitants of the Nightlands surged forth into the civilized lands. Armies of grey-skinned and bloodless corpses, animated by negative energy and motivated by an absolute hatred for anything that breathed, surged forth from the darkness beyond the edge of the world, and they brought that darkness with them. Equipped with dread magics and weapons that defied imagination, the armies of the dead quickly overwhelmed the sunlit lands. Where they went they stole the very sun from the sky, casting the world into freezing night. Even the greatest of nations fell before these invaders, and the most ancient of empires became as chaff before the wind.
Some few survivors remain to rail against the dominion of the dead. Although civilization has crumbled around them, although it would seem as though their goddess has abandoned them, although the sun itself has been extinguished, they fight on, knowing that surrender means oblivion—or worse.
Uldrus is a heroic fantasy campaign with a significant amount of supernatural and psychological horror thrown into the mix. It uses the D&D 3.5 game engine, but utilizes a fair number of rules from D20 Modern rule set (Call me crazy, but I always really wanted to see a fight between an ancient dragon and jet fighters, and an armored knight going toe-to-toe with a tank).