The Sword of Secrets author has released another challenge, using the same hardware: Nexus
It’s hard to find a way to mix fun and security for the masses, but I think Gili (the maker of the Sword) succeeds. The Nexus challenge is more javascript, and essentially zero hardware (unless you want to crack the private signing key using power analysis with a ChipWhisperer or similar), a has a storyteller’s touch.
First post has link to the sword’s website (which links github, etc.).