Little Alchemy 2 — start with four elements, discover 700+ things (opens destination in a new tab)

I dug up Little Alchemy 2 — you start with just earth, air, fire and water, and mix them into everything: mud, lava, swamp, energy... then life, then philosophy, then somehow a lightsaber. I lost a good hour making a Yeti. Free, no sign-up, dangerously moreish.