Players take turns filling in line segments on a grid, trying to enclose boxes. Typically closing a box allows you to play again, encouraging a gradual escalation by building corridors that can be claimed all at once. Strategy mostly boils down to Nim, picking when to bite and claim boxes. It'd be nice to find a variant with a little more strategy.

Played from a fairly young age on prayer cards at church. I don't remember where I learned this.