Amidst is an Open Source app to display an overview of a Minecraft world, without actually creating it.

Amidst features:

render an overview of a world from a given seed and Minecraft version
save an image of the map
use a save game
display biome information
display slime chunks
display end islands
display the numerous other structures such as world spawn, strongholds, temples and more
find individual blocks or mobs like
diamond ore
cows