  We present the first three-dimensional fully kinetic electromagnetic
relativistic particle-in-cell simulations of the collision of two
interpenetrating plasma shells. The highly accurate plasma-kinetic
"particle-in-cell" (with the total of $10^8$ particles) parallel code OSIRIS
has been used. Our simulations show: (i) the generation of long-lived
near-equipartition (electro)magnetic fields, (ii) non-thermal particle
acceleration, and (iii) short-scale to long-scale magnetic field evolution, in
the collision region. Our results provide new insights into the magnetic field
generation and particle acceleration in relativistic and sub-relativistic
colliding streams of particles, which are present in gamma-ray bursters,
supernova remnants, relativistic jets, pulsar winds, etc..
