There have been many posts here based on code from the book Programming The Finite Element Method, with the Fortran code either translated to VBA, or with VBA links to compiled Fortran Code. I recently discovered:
This Julia package currently contains the programs in chapters 4, 5 and early sections of 6 as described in “Programming the Finite Element Method” by I M Smith, D V Griffiths and L. Margetts (PtFEM).
Another recent Github site with open source (Python based) FEA code is:
PyNite is a library for structural engineering that creates and analyzes 3D finite element models of frames, trusses, and beams. For information on how to get started with PyNite please visit the other pages in this wiki! You can also have a look at the “Examples” folder for examples of how to use PyNite.
Both sites are works in progress, but already contain much valuable open source code.