freeFEM.org
Science, Math, Numerical Analysis, Software - FreeFEM. Free general PDE solver driven by a user friendly language.
https://freefem.org/
GNU Octave Repository
Octave-Forge is a collection of packages providing extra functionality for GNU Octave.
https://octave.sourceforge.net/
The Netlib
Science, Math, Numerical Analysis, Software - Netlib. Searchable repository of free numerical software.
https://www.netlib.org/
Foundations of Computational Mathematics (FoCM)
Science, Math, Numerical Analysis - Foundations of Computational Mathematics (FoCM). A nonprofit organization that supports and promotes research on foundations of computational mathematics.
https://www.focm.net/