  PHAST is a software package written in standard Fortran, with MPI and CUDA
extensions, able to efficiently perform parallel multicanonical Monte Carlo
simulations of single or multiple heteropolymeric chains, as coarse-grained
models for proteins. The outcome data can be straightforwardly analyzed within
its microcanonical Statistical Thermodynamics module, which allows for
computing the entropy, caloric curve, specific heat and free energies. As a
case study, we investigate the aggregation of heteropolymers bioinspired on
$A\beta_{25-33}$ fragments and their cross-seeding with $IAPP_{20-29}$
isoforms. Excellent parallel scaling is observed, even under numerically
difficult first-order like phase transitions, which are properly described by
the built-in fully reconfigurable force fields. Still, the package is free and
open source, this shall motivate users to readily adapt it to specific
purposes.
