Materializr

Materializr is real parametric solid modeling on your iPad.
It is built on the same industrial B-rep geometry kernel used by
professional CAD packages, wrapped in a touch-first
interface designed for makers.

Sketch on any face or plane, pull your sketch into a solid, and keep
editing any step of the history later — even after closing the project.
When your part is done, export an STL and print it.

Materializr is free and open source. There are no accounts, no
subscriptions, no ads, no locked features, and your designs never leave
your iPad. If it earns a place in your workflow, an optional Supporter
tip helps keep development moving.

Materializr is developed in the open under the GPLv3. The complete
source code, documentation, and community are at
github.com/materializr-cad/materializr