Ah, I forgot my favorite low-tech setting: a world named 567-908.
Also known as Shvreeyiyi (or something like that), it's home to a low-tech race of critters who had two large empires in the past, and are just coming out of a cultural recession. And the players have made the first contact with them since the pre-Maghiz Darrians.
Their civilizations never reached TL 3, and maybe not even TL 2. Their first empire, called "The Sun Worshipper Empire", centralized agriculture, worked distant mines for bronze, and lived on extensive grassland plains along the northern shore of a vast, shallow sea. Running their history, from large groups of warring nomads to the famine and final collapse of the empire, could be a memorable epic. Players could play key heroic figures through each phase of civilization, or could play it as a strategy game where they build up competing city-states and eventually manage the entire shebang, seeing how long they can avoid disaster. Perhaps Mesopotamian.
The second empire, which came much later, could be played in the same way, though with more of an Iliadic twist to it: survivors from the first empire struggled on for generations before planting the seeds of the new, improved empire across the waters. This one would be more rugged, with a more challenging existence, for it lived in more mountainous regions and had to carve a niche between the mountains and swamps for survival. This empire also progressed farther along the tech tree, and had superior watercraft, giving a completely different feel to the game -- more like Greece than Mesopotamia.
But wait, there's more! The Retreat offers yet another opportunity for adventure. After the second empire fell, the last vestige of civilization is the Retreat, a self-contained community in the mountains, the last vestiges of a faded culture. This plays more like a Dark Ages setting, where resources are spent on preventing barbarian hordes from destroying the last city. More than ever, heroic quests can restore the morale of an embattled community. There are enemy leaders to overthrow by cunning or open warfare, potential allies beyond the walls, and tokens from the former empire -- out there, somewhere -- to help restore faith and unity of purpose.
Ah, and finally, there's the Contact setting, which you can lift right out of Adventure 10, Safari Ship. A group of hapless adventurers agree to crew a safari ship for a wealthy businessman, and end up discovering the an unknown alien race. If they play their cards right, the players could end up becoming viceroys for the entire system, set up their own little starport, complete with a few token defenses... and end up changing the entire political demographics of District 268 in the process.