I have installed via port games/prboom (doom-engine) but it has installed as dependency to run, games/doom-data, which installed the non-free Doom shareware. Why do it not use free doom as a free-software dependency? I have used
pkg_deinstall -f doom-data
and I removed it, and prboom works fine with the freedoom .iwad which I have downloaded from here http://freedoom.github.io/download.html.