By navigating with a mouse through an infinite number of trees on Dryad, virtual world enthusiasts can create the trees of their dreams. Image courtesy Vladlen Koltun Vladlen Koltun

Stanford computer scientist Vladlen Koltun is giving away trees. Millions of them. They’re 3-D trees that can be downloaded, viewed from any angle, and planted in virtual worlds.

Thanks to their complexity, virtual trees are enormously difficult (and expensive) to create from scratch. But Koltun’s Stanford Virtual Worlds Group incorporated data from botanists into a mathematical engine that generates trees by defining about 100 different attributes (such as the thickness of the trunk, or the size of the leaves), each of which is infinitely variable. You can try out the new program, called Dryad, simply by navigating with a computer mouse through the program to choose the tree you want.—Dawn Stover

_Image: Stanford Virtual Worlds Group