The Maya Colonize The Caribbean?
Still self-banned from the alternate-history forum, but I found a cool discussion thread leading into a new timeline. Behold "Maya Colonization of the Caribbean"!
The gist of it is that the Maya develop outrigger canoes in the late pre-classic/early classic period. The Maya spread out into the Caribbean islands, with the technology spreading ahead of them and getting adopted by the Taino people, the tribes that in real history greeted Columbus and suffered greatly for it. The end result is a Mayan thalassocracy controlling the Caribbean basin, including major islands like Cuba, Hispaniola, etc. as well as the mouth of the Mississippi River in what will become the United States. Although there's a good bit of preliminary discussion, the actual alternate timeline starts here.
In real history, the Maya urban civilization (the Maya people are still there) collapsed due to overpopulation and resource exhaustion, but with the improved sailing capability and the trade routes existing this time around that didn't in real history, the surplus population moves out into the Caribbean islands. Eventually expansion becomes more land-based as the mainland stabilizes and the Maya civilization (they were decentralized city-states, like Greece, so it's not one giant empire) spreads further down into Central America and even onto the Pacific coastline.
By the time Columbus's ships arrive (nothing that changes in the Western Hemisphere is realistically going to affect the East unless the Maya manage to contact the Vikings, who would have to travel much farther south than they did in our history), civilization in the region has advanced well beyond the Taino chiefdoms Columbus encountered.
Not sure if the writer plans to depict what happens after Columbus's ships arrive (it ends with their arrival), but what's there is pretty cool.