Several mathematical libraries developed in the years 1970-1990 remain popular in the geophysics community. These libraries, listed below, are available for downloading here on GitHub: NCAR Classic Libraries for-Geophysics.
All of these library routines are written primarily in Fortran 77. Their internal implementation does not always conform to the Fortran Standard. FISHPACK90 provides a Fortran 90 interface to the FISHPACK routines. Only MUDPACK is written with parallelism in mind; it uses OpenMP directives for shared-memory parallelism. The other libraries were designed to run on a single processor.
These libraries represent many person-years of development, and though they are no longer under development, NCAR continues to make them available to the public at no cost under a software licensing agreement. The libraries are best suited to Linux and UNIX environments and require a directory structure, tar, and gmake commands.