A few years ago I came across an unusual game system created by Tony Dowler, initially created as a way of designing dungeons and cave systems for Dungeons and Dragons it later developed strange hybrid of creation toolkit and solitaire game.

The game is played in a series of successive ages:  

The Primordial Age: In this era the land is developed and sets the stage for the future develop of the dungeon, mineral reserves and ancient monsters lurking in the dark are all things that appear here.

The Age Of Civilisation: One or more precursor civilisations now come to the land each with their own unique rules and develop over a number of rounds until they are wiped out by disaster, monsters, war or they cause The Great Disaster that is a decade of cataclysm that last a decade.
In the original ruleset Dwarves, Dark Elves and Demons are the available though several others have been created by the community. 

The Age Of Monsters: Monsters now roam into the ruins of the destroyed civilisations and surface kingdoms take root, monsters are separated into three different classes:
Delving groups which represent intelligent ,well organised creatures such as Druegar and Hobgoblins.
Breeding Groups which are monsters that rely on replacing losses quickly to thrive and survive these represent Kobolds, Orcs and Goblins.
Alpha Predators these are the largest monsters of the dungeon seeking to eat or rule all others, Dragons, Fire Giants and Owlbears all come under this category.    

Each round now representing a year these monsters roam and expand their territories, fighting each other or raiding the Surface Kingdoms, on occasion adventurers and wandering monsters venture into the depths seeking treasure and glory with mixed success.
The Age Of Monsters comes to an end when the surface kingdoms are wiped out or a single monster group obtains enough treasure to begin the Age Of Villainy.

The Age Of Villainy: An Alpha Predator has grown in power or strength to become a menace to the whole region or a powerful creature of individual new to the area attracted by either the wealth of its inhabitants or the devastation they have cause. As these villains seek to consolidate their power adventurers now arrive in droves each year attracted by the growing rumours and tales of those who return. The Age Of Villainy ends only when the Arch Villain is victorious or lays slain.

The basic mechanics are relatively simple consisting mostly of random tables and If statements, in spite of this the slow build up of history of your dungeon can bring it to life and makes reading chronicles of other peoples dungeons quite engaging.    

If you'd like to see an example of play then watch the following video by GreenGoat:

A free version of the game minus its artwork and some extended details is available over at Planet 13 or for direct download here. 
If your interested in purchasing it then it can be acquired at Planet 13 or at Tony Dowlers blog.

For further posts on How To Dungeon here are links to:
Dsyon Logos Muck Dweller Civilisation 
Silverain Kobold Civilisation
The Great Spider Civilisation