preCICE (https://precice.org/) is an open-source coupling library for partitioned multi-physics simulations, including, but not restricted to fluid-structure interaction and conjugate heat transfer simulations.
Several FE libraries already have adaptors for preCICE, see the Overview of Adapters section.
yes, preCICE is a cool tool, making life easier when you want to couple different solvers , and it has a rich user community as well, but unfortunately, there is no adapter yet developed for FreeFEM, meaning that FF users cannot take advantage of it for multi-physics simulations.