... of charged "trapped" particles under the influence of EM Fields and there mutual Coulomb interaction.
Simbuca is easy to read and understand and can be tweaked to your personal needs.
It has been applied to simulate different types of particles: for example antiprotons, positrons, 39K+ , highly charged ions, negatively charged particles.
Simbuca also has been applied to simulate Penning/Paul traps, Mr-TOFs, RFQs, ...
More info on the wiki: https://sourceforge.net/p/simbuca/wiki