Bukkit

The multiworld plugin made by ferrybig

Creates cleanroom-style flat world generator with fully customizable layers. It can also be used to create empty space maps!

Nothing but void!

PlotSquared

A Skyblock Plugin

Pre-generates chunks, quickly, efficiently, and safely

Provides automated plots with protection (MultiWorld support)

Exotic Garden

IslandWorld - Survive on small isle

This plugin allow full control of normal world generator

A simple void world generator.

uSkyBlock

Create massive trees in Minecraft! Choose your own sizes and block types!

A plugin that makes your server lag free.

Completely overhauls the End dimension with new biomes, structures, bosses and more!

An Automated Hunger Games plugin!

CityWorld

Its a plugin, but its mod-like: New mechanics, new worlds, custom bows and strucutres, faster game, survival reinvented.

IslandCraft modifies the terrain generation to create an ocean with many islands; each island is a single biome.

This is a basic world generator that creates empty worlds. It's lightweight, easy to use, and very basic.