Little Alchemy 2

You start with four basic elements — fire, water, earth, air — and combine pairs of them to discover new items, building out a list of over 700 possible combinations. Some pairings are obvious once you think about them: combine two of the basics and you'll usually land on something sensible like steam or mud. Others require a genuine leap in logic, like figuring out which animal goes with which environment, or what happens when you introduce a human into the mix. There's no timer or fail state and no wrong move to punish, so it plays out as patient trial and error rather than anything competitive, and it's fine to walk away mid-list and pick it back up later.