80s and 90s kids will remember this, and it's making a comeback as a novelty item. No storyline, no visual and auditory stimuli, just a simple challenge to hook all the rings in the posts (extra points for achieving color patterns), so it's up to your imagination to fill in the rest. Real randomness, too, not subject to some random number generator. A real zen gaming experience. Pros: no batteries needed. Cons: risk of water spillage, occasional refills needed.

From a game design perspective, this is a fine example of how to set up progression, all done at various levels -- the abilities, the opponents, the character stories, and the location reveals. Not too difficult in game mechanics but does take time to complete. From Google Play. Caution / spoilers: some stories touch on death and suicide, and there are some creepy visuals and characters. Be aware when letting kids play, as you may need to give them some guidance.

An older title which I missed the first time around but recently discovered. Makes one think about how subways are designed.