The best replacement for fortran is c.

The best alternatives to fortran are rated as following:
★★★★★  c
★★★★★  matlab
★★  cobol
★★  c++
★  visual basic
★  pascal
★  julia
★  ada
★  numpy
★  algol
★  fortran
★  matlab speed
★  c++ speed
★  python speed
★  lisp
  c faster
  c++ performance
  assembly
  qbasic

Your alternative for fortran is not listed? Suggest!
Speaking about fortran, one probably shouldn't forget about gui.

Other search terms related to fortran and their ratings are:
★★★★★ gui
★★★★★ abaqus
★★★★ code blocks
★★★★ imsl
★★★ mpi
★ microsoft visual studio
You have in mind a companion for fortran and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fortran in all years. Click on graph for more.
fortran
c
matlab