When I'm not working and not making indie games, I make open source libraries for indie games programmers. Since I use all of those libraries myself, I try to keep them in good shape, some of them already proved to be useful to some people which makes me happy.
detect-collisions
TypeScript Collision Detection Library for Points, Lines, Boxes, Polygons, Ellipses and Circles, with rotation, Raycasting, Bounding Volume Hierarchy and Separating Axis Theorem