ABSTRACT. The paper presents SIAMOA, a system dedicated for design, debugging and visualisation of algorithms. It combines elements of an algorithm visualisation system and an environment for visual programming. Programs may be created graphically by connecting modules represented in form of icons. Individual modules correspond either to sequences of operations written in a traditional, textual form, or to complex blocks of operations created graphically. The main concern of the visualisation of the algorithm execution process is data visualisation; it may be done as a basic or a synthetic one. The architecture of the visualisation engine has been designed with use of the P.Os.T. model, previously used to build interactive platforms for simulation of industrial processes.