KMC/DMC are general purpose programs for the simulation of chemical reactions taking place at crystal surfaces. The used simulation method is a Discrete Event Simulation with continuous time. In the literature this is commonly called a Dynamic Monte Carlo simulation (DMC) or Kinetic Monte Carlo simulation (KMC). The general purpose nature of the program is visible in a clear separation between model and (simulation) method. The simulation model is specified in terms of surface structure and changing patterns, reflecting the reactions taking place at the surface. Several methods can be employed on the model differing only in simulation speed and memory use.