Fill Tool

This mod adds a basic terraforming tool.
It lets you mark two points (left/right click) and then use the /fillblocks [block] [optional:meta] command to fill the area with the desired block type.

To replace only specific blocks: /replaceblocks [newBlock] [oldBlock] [optional:meta]
To scatter the desired block type across the target zone: /scatterblocks [block] [percentage] [optional:meta] (percentage is a "per block" chance to be replaced with the desired block.)

Sunshine and flowers not included.

This tool is only usable in creative mode and while holding it. (Meaning you can have multiple tools for different areas.)
The [block] parameter is using the new block identifiers, ie “minecraft:dirt“. Or “minecraft:air“.
This should also work for any other mods that you know the names of. (You can crouch-use the tool to get the block name.)