What visualization libraries are available for Fortran?

Just to make this list, a bit more complete ...

• PLPLOT
• GINO Suite
• Winteracter
• NCAR (outdated)

There is also gtk-fortran.

gtk-fortran offers also an interface to PLplot (>=5.13 in the GTK 3 branch).

Free: Mjograph (2d plots only) and Veusz (2d and 3d plots)

Perhaps you can generate csv or simple space-delimited files with your Python/Compiled-Fortran code, and process using 2d plotting software like Mjograph and/or 2d/3d software like Veusz. Mjograph is only available via Mac and/or Java platform. Veusz is scriptable with Python, it was built using Python with Qt & Numpy, in fact the save file is just a plain Python script, and is comparable to gnuplot (at least in terms of ease of use). The tutorial with veusz clearly shows what the capabilities are. I like that it starts you off with the GUI, but you can wean off to pure scripting afterwards.

Mjograph: http://www.ochiailab.dnj.ynu.ac.jp/mjograph/ Veusz: https://veusz.github.io/

Veusz seems a little more natural compared to dumping data into Matlab or Mathematica. At least if you are used to pushing python and Fortran around with Bash scripts on linux.

If you insist on 3d data, I would take a second look at DISLIN, it can work quite well depending on what you need to visualize. The license is quite affordable for commericial-use. If using for academic use it's free.