EARN 3.1 Brain and Fancy lights :D
Starting with EARN 3.1, Core can be separated from Service Hubs.
Delivery Monitor allows you to notice the issues on your base.
Signal debugger can be used for checking signals. Would help you understand how everything works if you're into Factorio Circuits.
Core is still included in the Rail Network Connection blueprint on my Quick Start Base
Check EARN v3 Documentation for more info about the combinators inside the Core