We present a distributed algorithm animation system called Catai (for Concurrent Algorithms and data Types Animation over the Internet). Among the features of this system are a low e ort required for animating algorithmic code, and the possibility of embedding animation clients in standard Java-enabled Web browsers. We believe this to be a good compromise between two di erent viewpoints: the programmer's perspective, which typically includes the goal of animating e ciently and unobtrusively a given algorithmic code, and the user's perspective, which can bene t from interactive, easy-to-use, distributed and cooperative interfaces.