World Edit

World Edit is an easy-to-use in-game world editor for Minecraft, supporting both single player and multiplayer. It is made by sk89q. It is created in 2011. It requires Minecraft Forge, but there is a separate Bukkit plugin too. Through a combination of commands and "brushes," you can sculpt your world or simply perform numerous terraforming tasks.

Here are some functions :
 * Quickly create, replace or delete thousands of blocks in seconds
 * No longer waste time doing mundane activities like fix badly flowing water!
 * Quickly create basic shapes like spheres, cylinders, and so on
 * Copy areas, paste them, load them, and save them as .schematics
 * Do cool things like input mathematical expressions to generate terrain
 * Use "brush tools" to carve out mountains, ravines, and so on
 * Use your compass to quickly teleport to areas by left clicking or using /jumpto
 * Choose an area and have it instantly restored from backups
 * One of Minecraft's oldest surviving projects (since Minecraft Alpha)!

Tutorial
ShawnVMartin Tutorial