OpenSCAD

OpenSCAD builds solid models from a script rather than a drawing canvas. You write statements that create primitives such as cube, sphere, cylinder and polyhedron, combine them with the solid geometry operations union, difference and intersection, and place each piece with translate, rotate and scale. Two-dimensional outlines are raised into solids by linear and rotational extrusion.

Because the model is code it is parametric by construction: variables carry the dimensions, modules package reusable parts, and loops and conditionals produce repeated or variant geometry. The Customizer panel turns top-level variables into form controls, so a design can be adjusted without editing the script. A fast preview shows the shape while you work; a separate full render computes the exact mesh that export needs.

Models are written out as STL, OFF, AMF and 3MF for printing, and as DXF or SVG in the two-dimensional case. The approach suits mechanical parts defined by measurements. It is a poor fit for sculpted or organic shapes, and there is no way to grab the model and pull it with the mouse.