Deployer

Deployers use items in much the same way a player does.

A Deployer has nine slots in its inventory. (You can feed it with tubes). Upon receiving a redstone pulse, it examines its contents in order (left-to-right, top-to-bottom), and when it finds a non-empty slot, it emulates a player's right-click action when holding this item. It can place blocks, fill buckets, empty buckets, till dirt, make fire, and do almost everything that a player can do—except for breaking blocks, which is what a Block Breaker does.