MCEdit is a free world editor mod for Minecraft.
Do not use this tag for technical issues with this mod, eg. MC crashes when …
MCEdit is a mod for Minecraft. It's a third party tool available for free to download (8mb), licenced as open source. The current version is 2.0, but the mod is still under big development.
The mod is defined as a "saved game editor for Minecraft" - it allows you to use new edit tools, in-world and out-of-world. It also supports editing for/on your MC servers.