An architecture suitable for running on processing systems of limited processing power is disclosed. The architecture facilitates the portability of applications and optimises the use of CPU and/or memory resources. The architecture is embodied in novel data structures and applications which may be compiled into an extremely low footprint and optimised machine code. Also disclosed are tools for developing applications and particular applications of the architecture. The invention is particularly useful in the context of set-top-boxes, where it facilitates production of interactive games and the like which were previously not practicable.