See also the 25 Holes Challenge.
You may win a silver dollar!

This sweet and innocent-looking set of 21 V-shaped trominoes (3 squares each) can entertain a four-year-old with simple patterns, yet infuriate a grown-up expert with tough challenges. Math professor Norton Starr originally commissioned this set to demonstrate proof of a theorem—that an 8x8 grid can be filled with V-trominoes no matter where you leave the empty space. We coupled this puzzle with a color-separation feature, then added an original concept by Oriel Maximé, of filling the Vs on grids around strategically placed barricades. The 28 "Bends" layouts cover four levels, from Easy to Expert. Other challenges and game rules are included. A feature discovered later and added in the second edition of the book is a pretty alphabet. All acrylic, 7 tiles each of 3 luminous transparent colors in 7" tray with engraved grid lines. You can choose from three color combinations. Ages 4 to adult, 1 or 2 players. $42

How cool is this? This solution can easily transform into any tetromino (the 5 shapes made of four squares), also known as Tetris pieces. If old Archie only knew!

This 14-tile dissection is the oldest documented puzzle in the world, and the decipherment of Archimedes' rediscovered manuscript is a hot topic among historical scholars and mathematicians. Also known as the Stomachion, it even made the front page of the New York Times, December 14, 2003. Luminous transparent colors in a sculpted 7" acrylic tray. Long unanswered:  Just how many ways can this square be solved? On October 31, 2003, Bill Cutler's program found the full answer of 536 distinct solutions. (Read the full story.) How many other convex shapes can the 14 tiles make? Bernd Rennhak in Germany found all 637 solutions. He also found that the set can solve 13 of the 14 tetratan shapes. The permutations are staggering. An amazing fact is that each tile's area is a whole number, based on the square as a 12x12 matrix. That gives each of the 3 colors we added an equal share of the total area. Here truly is ancient genius made visible. Some of the tiles have sharp points, so we recommend ages careful 10 to adult.$42

36 acrylic pieces include all the shapes of 6 squares joined ("hexominoes"). Each piece has a name. They are sized to be compatible with Poly-5, for those who want the extra excitement of combining the whole series. The 8˝" tray and game grid accommodate four strategic games and hundreds of puzzles. Sextillions is available in several color combinations. For its 25th anniversary in 2009, we gave it a frosted silver frame and center, and a special "25" solving challenge (.pdf, opens in new window). Suitable for 1 to 6 players, ages 12 to adult. $65

This 15-piece two-color set continues to delight us with its variety of shapes and color symmetries, even years after we originally explored it. The all-acrylic, handfitted tiles are one and two right triangles in size (one sample shown), with plenty of puzzles both in and outside of their 8˝" tray. Choose from 6 color mixes. For its 25th anniversary in 2012, we added a touch of silver. Suitable for 1 or 2 players, ages 8 to adult. $65