lib

GSL - GNU Scientific Library

https://www.gnu.org/software/gsl/

eigen

http://eigen.tuxfamily.org/index.php?title=Main_Page

libigl - A simple C++ geometry processing library

https://libigl.github.io/

CGAL

https://www.cgal.org/

ShapeOp

https://www.shapeop.org/

Wykobi

http://www.wykobi.com/tutorial.html

https://github.com/google/s2geometry

Boost.Polygon library

The Boost.Polygon library provides algorithms focused on manipulating planar polygon geometry data.

https://github.com/pmp-library/pmp-library/

https://github.com/bulletphysics/bullet3

https://github.com/erincatto/box2d

https://github.com/skyrpex/clipper