With the approach of exascale computing era, particle-based models are becoming the focus of research due to their excellent scalability. We present a new code, Slurm, which implements the classic particle-in-cell algorithm for modeling magnetized fluids and plasmas. It features particle volume evolution which damps the numerical finite grid instability, and allows modeling of key physical instabilities such as Kelvin-Helmholtz and Rayleigh-Taylor. The magnetic field in Slurm is handled via the electromagnetic vector potential carried by particles. Numerical diffusion of the magnetic flux is extremely low, and the solenoidality of the magnetic field is preserved to machine precision. A double-linked list is used to carry particles, thus implementation of open boundary conditions is simple and efficient. The code is written in C++ with OpenMP multi-threading, and has no external dependencies except for Boost. It is easy to install and use on multi-core desktop computers as well as on large shared-memory machines. Slurm is an ideal tool for its primary goal, modeling of space weather events in the heliosphere. This article walks the reader through the physical model, the algorithm, and all important details of implementation. Ideally, after finishing this paper, the reader should be able to either use Slurm for solving the desired problem, or create a new fluid PIC code.

Accepted to the special issue "Advances in the Numerical Simulation of Plasmas" of the Computer Physics Communications