One possible scenario:
The Ottoman Turks (who were the first empire to use gunpowder on a really large scale for warfare and sieges) are not successful in conquering Constantinople in 1453. Their empire crumbles apart after a few decades.
The Byzantines rise again (as they did many times before). Spices, silk and other goods keep on flowing from Asia into Europe via the Silk Road.
No need for Portuguese, Spaniards, Dutch, Britons and French to look for maritime ways to acquire the riches of the orient.
No Columbus, no discovery of the Americas.
The middle ages never end. Most people still live as farmers and use slings to scare away predators and thieves from their lands.
No internet, no slinging.org, but a lot of excellent slingers.