EXCALIBUR - a Monte Carlo program to evaluate all four-fermion processes at LEP 200 and beyond*

A Monte Carlo program is presented that computes all four-fermion processes in e+e - annihilation. QED initial state corrections and QCD contributions are included. Fermions are taken to be massless, allowing a very fast evaluation of the matrix element. A systematic, modular and self-optimizing strategy has been adopted for the Monte Carlo integration, which serves also as an example for further event generators in high energy particle physics.