Lworld is a computer graphics animation system based on L-systems, a parallel rewriting technique used primarily in computer graphics for plant modeling. Because rulebased programming is a powerful technique, we use it as a basis for a general-purpose animation system. We describe the architecture, the features, and the programming language of the animation system. It is particularly well suited to model fractal curves, plants, fractal landscapes, group animation, visualization, and evolutionary optimizations. Lworld allows users to create real-time animations as well as raytraced image sequences for further movie production. It is freely available, and runs on PCs.