  We present a new multi-fluid, grid MHD code PIERNIK, which is based on the
Relaxing TVD scheme (Jin and Xin, 1995). The original scheme (see Trac & Pen
(2003) and Pen et al. (2003)) has been extended by an addition of dynamically
independent, but interacting fluids: dust and a diffusive cosmic ray gas,
described within the fluid approximation, with an option to add other fluids in
an easy way. The code has been equipped with shearing-box boundary conditions,
and a selfgravity module, Ohmic resistivity module, as well as other facilities
which are useful in astrophysical fluid-dynamical simulations. The code is
parallelized by means of the MPI library. In this paper we introduce the
multifluid extension of Relaxing TVD scheme and present a test case of dust
migration in a two-fluid disk composed of gas and dust. We demonstrate that due
to the difference in azimuthal velocities of gas and dust and the drag force
acting on both components dust drifts towards maxima of gas pressure
distribution.
