First invented in 1880, this pocket-sized numerical puzzle became wildly popular in the 1930's. Now it's making a comeback with this retro version, in polished stainless steel with red and white enamel. Slide the square metal number tiles around in the tin until they're in numerical order, or reverse numerical order, or any of the other 30 possible puzzle combinations included in the instruction booklet. Or, make up your own sequence with the numbers 1 to 15 and try to work it out on the puzzle. A hands-on way to hone critical thinking skills, and open-ended enough to grow with your child. (ThinkFun, $9.87)