Show HN: Popkern – open-source CAD kernel with G2 corner blends, browser IDE

Popkern is a free, open-source kernel for building solid CAD models through short Rhai scripts, with an interactive browser environment and support for local command-line workflows. Its central idea is to make sophisticated geometry available through code while keeping models editable and reproducible: larger projects use numbered migration scripts, so designers can track and replay feature history or revise earlier steps. Projects can be exported as Popkern documents or STEP files. Demonstrations include a detailed six-axis robot arm, gearboxes, ISO-threaded fasteners, an impeller and springs. The kernel supports booleans, fillets, chamfers, sweeps, revolves, lofts, shelling, constrained sketches, STEP import and export, and a feature tree with undo. A particular focus is smooth corner blending: a curvature-continuous cap joins differing radii without disrupting zebra-stripe curvature visualization.

The project presents itself as usable but still early, and invites users to report parts it cannot build so failures can become tests. Its code is produced by AI agents under human direction, with changes required to pass thousands of automated tests and kernel validation; results are also compared with OpenCASCADE where possible. Operations that cannot yield valid solids are designed to explain the failure instead of returning broken geometry. The kernel is licensed under AGPL-3.0, while an explicit exception leaves users’ scripts, models and exported files theirs. The intended audience is makers and CAD developers seeking a scriptable, open alternative, especially those willing to test its current capabilities and help expose gaps.