Minecraft's "copy block" system.

[mrwallace888]

There's a thing in MC, middle-click, I think, where it adds the block you're looking at to your inventory.

Could be useful for Blockland, most definitely. Also one where it copies the color you're looking at.

[Ad Bot]

[Abstath]

There is an add-on to copy a brick's colour. Right-click with the spray can while looking at a brick.
Not sure if there's already an add-on to copy a brick, though.