XC is an open source FEA program designed to solve structural analysis problems.
It's all about developing tools that allow us to keep going forward (much in the sense of designing for strength, economy and beauty) instead of repeating the same old solutions but in a faster way.
How?; allowing to merge the code with other software libraries: machine learning, neural networks, 3D modeling, material libraries, computation fluid dynamics,...
It's based on Python ( script language), Opensees (analysis kernel), CGAL (computational geometry), VTK and matplotlib (for the graphics stuff) and LaTeX for text output.
The program can solve various types of problems, from simple linear static analysis to complex nonlinear simulations. It has a library of finite elements which allows to model various geometries, and multiple material models, allowing its application in various areas of structural analysis.
You can take a look into the Python API documentation here, and to the C++ API documentation here.