A few entities that help do some small utility things:

• Circuit network transceiver - Send and receive circuit network signals over any distance (and between surfaces)
• Daylight sensor - Outputs current light to circuit network
• Motion sensors (Enemy and friendly variants) - Detects motion and sends a circuit network signal
• Pollution sensor - Outputs pollution percentage to the circuit network
• Pressure plate - Outputs a circuit network signal when stepped on
• Remote explosives (TNT) - When the circuit condition is met, kaboom
• Sign posts - Write messages to yourself or your friends
• Torches - Burner illumination for the early game
• Tinderbox item - Early game way to start fires
• Long-range delivery drones - Deliver items a long long way. Drone Graphics/Animation by Sacredanarchy.