Dataplot | NIST is public domain and contains a vast collection of statistical software in Fortran 77 last I looked. At least one version of DATAPAC is on github. Might be dated (or not). Used the interpreter heavily in the past but have not used it in recent years but it was accompanied by a very complete set of documentation as well as I remember it. Not sure if that is of interest or not, but it was all public domain.