The supplement "Beyond the Prism Pentad" deals with the world up until Free Year 11. Free Year 10, the Year of Friend's Agitation, includes the reappearance of Rajaat, the death of the Dragon and two other sorcerer-kings, as well as the exile of another. A great earthquake rocked the western part of the Tablelands, and Tyr-storms began to boil out of the Cerulean Storm in the Sea of Silt.
With the second boxed set, we cast our eyes both northward and westward, learning of two lost sorcerer-kings and their cities, as well as a sea far to the north, where some lizard men still dwell. To the west, we learned of a vast savanna, where a Kreen empire stood, and halflings, living on the cliffs, using strange, living, devices.
But all of this was the immediate aftermath of the Prism Pentad; the lava under the Cerulean Storm hadn't even cooled. Rise and Fall of a Dragon King told us that Hamanu would soon leave the city of Urik, not to return for a thousand years. The world had changed considerably since the first boxed set.
With this, I have laid out the course of the world in the next King's Age, starting with FY 1, when Kalak was overthrown, and continuing to FY 77, the Year of Desert's Slumber. This is a convenient spread of time for the people of Athas, who treat King's Ages much like we treat centuries. From this point, it is the 191st Kings Age. The heroes from the "Decade of Heroism" that started in FY 1 are dead; even Rkard, born during that decade, is now of venerable age for a mul. Save for some dwarves, most of those who lived in those days are now dead, or similarly aged. It is a time of stories, while life under the dark sun concerns the now.
This is based, in part, on the later supplements of the Dark Sun line; Beyond the Prism Pentad and the revised and expanded boxed set. It is not rules-agnostic, as I reference 2nd edition AD&D levels and, as above, life spans. However, it is very rules-light, with what it there relatively easy to convert into your system of choice. It is organized as a gazeteer, for ease of reference, but with a timeline at the end.
