  We give a full description of the code NBODY2 for direct integration of the
gravitational N-body problem. The method of solution is based on the neighbour
scheme of Ahmad & Cohen (1973) which speeds up the force calculation already
for quite modest particle numbers. Derivations of all the relevant mathematical
expressions are given, together with a detailed discussion of the algorithms.
The code may be used to study a wide variety of self-consistent problems based
on a small softening of the interaction potential.
