Doulairen is the Campaign World created by Steve Mossman. The Fourth Age is the most used, having had several campaigns in it, all based on 3rd edition Dungeons and Dragons. Mike Kirk also has run a campaign in the Fourth Age of this world, and Doug Hottinger has contributed some to the Fourth Age as well. The Sixth Age is the current setting for the campaign world, using a set of house rules based on a core d20 mechanic.
Ages of Doulairen
First Age - Known as the Age of Dragons.
Second Age - Known as the Age of Elves.
Third Age - Known as the Age of Heroes.
Fourth Age - Known as the Age of Fate.
Fifth Age - Known as the Age of Kings.
Sixth Age - Known as the Age of Elements.