  The self-gravitating systems are formed by particles interacting through
gravity. They describe structure formation in the universe. As a consequence of
the long range interaction of gravity, they are inhomogeneous even at thermal
equilibrium. We study the self-gravitating systems with several kinds of
particles and the self-gravitating systems in the presence of the cosmological
constant $ Lambda$. We formulate the statistical mechanics and the mean field
approach describing the gaseous phase. We explicitely compute the density of
particles and thermodynamic quantities. The presence of $ Lambda$ extends the
domain of stability of the gaseous phase. Monte Carlo simulations show that the
mean field describes the gaseous phase with an excellent accuracy. Scalling law
of the self-gravitating systems with several kinds of particles is found. At
the critical point the fractal dimension is independant of their composition
and is $1.6...$~.
