1. Single Player Commands

WorldEdit CUI Forge Edition Mod 1.12.2/1.11.2 provides a client-side user interface for the WorldEdit plugin allowing you to see your selected region in-game in real time.

Many of the world edit commands are in vanilla minecraft now. Specifically Clone and Fill, plus a bunch of variant rules you can use with them (like replacing only blocks of a certain type in the destination area, or only cloning blocks of a certain type FROM the original area).

Single Player Commands

The max size is lower, and there's no output to schematic file or any equivalent, but then they just added this in the latest major update so maybe that stuff's coming in 1.9., you can find fill and clone in the contents sidebar (to the right).