Blender… THE best piece of open source software developed to date . . .
that’s my hard opinion, but I can’t think of other examples where the open source community made a free application that could compete with $20,000 worth of software
(at 1st glance you’d be fooled into thinking it was just 3D modeling, animations, and VFX , but dig deeper and you’ll find some really cool stuff like 3D printing and dynamic physics simulation support)
Community made extensions for 3D printing