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Quote from grimallq
Assuming you want to use World Edit in singleplayer, it depends on which version of Miencraft you want to use.
For Minecraft 1.6.4 the best would probably be the Single Player Commands mod. There is a Forge version of it for 1.6.4 somewhere in their thread. Don't have the actual link on hand.
For Minecraft 1.7.2/1.7.10 the best is probably WorldEdit Wrapper for Liteloader.