If you don't think geometry can be fun, you're wrong. Behold Euclid The Game, an addictive addition to the pantheon of tools for internet procrastination.
The game puts players through basics of Euclidian geometry. It starts out relatively simple: to pass each level, you have to use basic tools of geometry—line segments, circles—to show how you can create an equilateral triangle or bisect an angle. But soon it gets more difficult, and you're being asked to trisect a segment or perform this task: "Construct two new circles of radius AB where each pair of the three circles is tangent."
When you complete each task, you get a friendly "Well done!" and you unlock the next level. The tools take some getting used to, but are relatively intuitive. And it turns out that playing around with lines on (virtual) paper is—contrary to what high schoolers in math class might think—really fun, especially when the alternative is doing actual work.
So, what are you waiting for? Check it out, and don't be a square—unless the game asks you to create one, that is.