ChatBox is a mod that just adds one block, one that "talks" to the players inside a radius. To activate give it a pulse of redstone, to craft it simply put cobblestone at the corners, iron at the sides and redstone at the center of a crafting table!
Change the minimum and the maximum radius and the formatting of the chat text in the config options. The name of the block can be changed just like chests, furnaces, command blocks, etc.
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