This virtual Erector set is sure to replace hours of work with play. A simple-looking Java program created by a London-based Web development company, it lets you change the characteristics of a two-dimensional line drawing made of joints and springs. Start with one of the preset models, like the Dirkjiggler or Wigglyworm, and use your mouse to drag it around the screen. Then go to the control panel and futz with the wave speed and amplitude to get your Wigglyworm jiggling out of control. Adjust the friction bar to slow it down, or throw on some more gravity — or turn gravity off entirely, using the pull-down menu across the top of the screen. Once you’ve delighted in the resulting spider-dance variations, make your own model from scratch. Giving your creation sprightly muscles and joints is harder than it looks, but you’ll get the hang of it by the end of the day. Hey, it’s not like you have anything better to do.