6: Better World Generation Mod
Similar to Biospheres but a little less specific, Better World Generation gives you a bunch of options as to how Minecraft generates the game world. These options include a switch back to the generation rules of the Alpha and Beta versions, an improved Superflat World, improved default and very large biomes, and something special.
One of the options to create a world is called “survivor island”, which strands the player on an island in the middle of the ocean with a little chest filled with some random stuff. Another is called “survivor sky island”, which puts the player on a significantly bigger, floating island. And the third one is called “sky dimension”, which puts the player into a game world made up of floating islands. You can get the mod at Minecraft DL.