Counterplays is a tile-stacking game that uses hexiamond-shaped tiles. A hexiamond is a piece composed of six congruent equilateral triangles, connected along their edges. There are 12 different hexiamonds. The game title is composed of them all (special thanks to Nathan Morse for this).
Counterplays is a brother game of SEVEN, Pent-Up and Stack-22, by the same designer. Players alternate turns placing one of their tiles according to some simple rules, trying to get the most of their pieces on the topmost layers when the game ends.
Note that some of the tiles are not symmetric, and can be placed either side up.