Non-linear chemical and excitable media exhibit a wide range of space-time dynamic: from well known circular waves to self-localized excitations. If we take a resting medium and change concentration of reagents or other parameters then diffusive or phase waves are generated and spread all over the medium. The waves interact one with another and form either dissipative structure or a precipitate. All micro-volumes of the medium update their states (local concentrations of reagents) in parallel. Thus, the medium can be thought of as a massive parallel processor, where data and results of a computation are represented by concentration profiles of the reagents. A theory of reaction-diffusion processors is still under development. In the paper we give an account of our personal experience in design of reaction-diffusion and excitable processors, mathematical models and working prototypes. Various aspects of reaction-diffusion computing are illustrated by actual examples of parallel solutions of various problems from computational geometry, optimization on graphs and communication networks, control of mobile robots and implementation of logical operations. Prospective material base for fabrication of reaction-diffusion and excitable processors is also tackled.