A Minecraft Map Editor... that runs in-game! With selections, schematics, copy and paste, brushes, and scripting. Use it in creative, or use it temporarily in survival.

WorldGuard lets you and players guard areas of land against griefers and undesirables as well as tweak and disable various gameplay features of Minecraft.

CraftBook lets you create magically extending bridges, compact Redstone circuits, complex Minecart mechanics, and much more... — all without a client mod and fully customizable by the server.