Accrete is a physical simulation of solar system planet formation,
originally published to Usenet-- probably comp.sources.unix-- in 1991
by Joe Nowakowski. This software is in the public domain.

This simulation works by modelling a dust cloud around a Sun-like
star, injecting a series of masses which collect dust, and form
planets. The simulation then determines what the planetary
environments will be like in terms of temperature, atmospheric
composition, and other factors. The system description is saved to a
file named "New.System".

WWW: http://sourceforge.net/projects/accrete