For those wanting to use Fortran 2018 features on Gfortran, the latest Gfortran 8.0 is very good to have.
Note that Ubuntu ≥ 17.10 is required for GCC/Gfortran 8 via this PPA.
add-apt-repository ppa:ubuntu-toolchain-r/test apt update apt install gfortran-8
For Ubuntu ≤ 17.04, GCC/Gfortran 7 is the newest available via this PPA.
If you want older versions of gfortran
apt install gfortran-6
Then select compiler version.
Gfortran is installed on Mac OS with:
brew install gcc
Install Windows Gfortran, GCC, Cmake, etc.