[starseeker]

Well, there's a lot - a few I happen to be familiar with:

Maxima: https://maxima.sourceforge.io/

Axiom: http://www.axiom-developer.org/

OpenCascade: https://dev.opencascade.org/

BRL-CAD: https://brlcad.org/

GRASS: https://grass.osgeo.org/about/history/

illumos: https://illumos.org/

Docker: https://github.com/docker

Torque: https://github.com/GarageGames/Torque3D