Here is a project that can be relatively easily made using two Spark Cores, a handful of wires, push-buttons, LEDs, and the Spark web IDE. The project relies on two Cores, "Core1" and "Core2". Each Core controls two LEDs. One's state ("SendLED") is dependent on a local push-button and is published to the Spark Cloud via Spark.publish(). The other LED's state ("ReceiveLED") mirrors the state of the "SendLED" on the other Core's board, pulling the published data using Spark.subscribe(). See the Fritzing diagram to reconstruct the hardware on a breadboard. The Core1 and Core2 code only varies slightly, but the system does need one copy of each flashed to one of the two Cores. It's amazing how fast the internet is at publishing and subscribing the state of the LEDs. Enjoy.
Entanglement in action