Isaac is an abstract strategy game for two players.

The game is divided in two different phases, placement and scoring.

During the placement, a player places one of his rectangular pieces on the available spaces of a 10×10 square grid board.

During the scoring, each player removes one of his pieces from the board, scoring a number of points equal to the number written on the removed piece times the number of pieces that lie on the row/column from which the piece was removed. A piece can be removed only if it is at least long as the longest piece already removed by the same player.

Each player uses his/her own counter to keep track of his/her points but the counter itself is placed on the board (that is, the board is also the score track). The presence of a counter on the row/column from which a piece is taken doubles the points scored. A player can decide to score less points than he/she earned, therefore allowing to place the score counter in a more convenient place.

You can play Foundations and Hari with an Isaac set.