You cannot have a fraction of a photon. So this is particle-like behavior. Whether you say it is a particle or acts like a particle is a matter of style. Light has both wave and particle characteristics. In that sense, the photon has zero mass.
Some people say zero rest mass to avoid any confusion.
You can use this to solve collision problems, for example a collision between an electron and a photon. It works just like an elastic collision in mechanics except that if the photon gives some energy to the electron, then the photon after collision will have a longer wavelength.