Abstract combinatorial game, usually played on paper, learned by many during childhood.
Start with a grid of dots, and two players take turns drawing lines between two dots adjacent horizontally or vertically. Completing a 1x1 box gains a point and another turn. It turns out to be quite an interesting and difficult game mathematically and computationally.
Sprouts is a topological pencil-and-paper game invented in 1967 by mathematician John Horton Conway (who also designed the computer game "Life") and Michael S. Paterson, both of the University of Cambridge in the United Kingdom.
The game of Sprouts and its joke variant Brussels Sprouts are described in Martin Gardner's book Mathematical Carnival.
In Tic-Tac-Toe, also known as Noughts and Crosses and Ticktacktoe, two players-- one drawing crosses, the other circles-- alternately make their marks in a 3 by 3 grid-like figure. The object is to be the first to make three in row.