I've recently run across a site from a kindred soul called MathPath, which is available in English and French. This site is full of math tricks and discussions that regular readers of this blog will find very interesting. Much like my own Be A Genius* site, MathPath lets you pratice the tricks you learn right on the site, such as learning to square numbers up to 125 in your head! There's also a program that automatically generates Magic Squares (PC only). He offers the complete Visual Basic project files for download, so perhaps some venturesome REALbasic programmer can create a Mac version.