This is a pyramid adaptation of the game Semaphore by Alan Parr, featured in the book book Mathematical Games, Abstract Games by João Pedro Neto and Jorge Nuno Silva. (Thanks to Lou Lessing and Nick Sula in the Starship Captains Facebook group for the name Stalagmite and the suggestion of using small, medium, and large pyramids in place of the green, yellow, and red tokens in the original rules).
Stalagmite is played on a 3x4 grid. It requires 12 trios in any combination of colors. Players take turns placing a pyramid in the grid. Small pyramids can be placed only on open spaces, medium pyramids can only be placed on small pyramids, and large pyramids can only be placed on medium pyramids. Nothing can be placed on a large pyramid. The goal is to complete a line of 3 of the same size with your move. Lines can be horizontal, vertical, or diagonal, much like Tic-Tac-Toe.
- Article on Semaphore: http://matheminutes.blogspot.com/2015/09/gaming-is-good-for-students.html