  We present the Fluid Transport Accelerated Solver, FluTAS, a scalable GPU
code for multiphase flows with thermal effects. The code solves the
incompressible Navier-Stokes equation for two-fluid systems, with a direct
FFT-based Poisson solver for the pressure equation. The interface between the
two fluids is represented with the Volume of Fluid (VoF) method, which is mass
conserving and well suited for complex flows thanks to its capacity of handling
topological changes. The energy equation is explicitly solved and coupled with
the momentum equation through the Boussinesq approximation. The code is
conceived in a modular fashion so that different numerical methods can be used
independently, the existing routines can be modified, and new ones can be
included in a straightforward and sustainable manner. FluTAS is written in
modern Fortran and parallelized using hybrid MPI/OpenMP in the CPU-only version
and accelerated with OpenACC directives in the GPU implementation. We present
different benchmarks to validate the code, and two large-scale simulations of
fundamental interest in turbulent multiphase flows: isothermal emulsions in HIT
and two-layer Rayleigh-B\'enard convection. FluTAS is distributed through a MIT
license and arises from a collaborative effort of several scientists, aiming to
become a flexible tool to study complex multiphase flows.
