Chunky

What It Is
This plugin pre-generates chunks in a defined area.
https://github.com/pop4959/Chunky
Useful Commands
chunky world [world] - select a world to chunk
chunky shape [shape] - define the shape of the area to chunk
chunky radius <radius> [radius] - define the size (X & optionally Z) to chunk.  Preface the radius with 
+ to expand on an existing area
chunky start - start the pregeneration process
Related Plugins
Chunky Border - set up custom world borders.
chunky border add - using the world, shape, and radius commands above to set a custom world border.