Tinker Desk is an offline browser modeler for simple prints. Add shapes, size them in millimeters, group solids and holes, and save a project file, an STL, or a 3MF.
Open this page, add a Box, and set its size in the Size inspector. File, Edit, Tools, and Print hold the rest of the model. Save the project with Save project. Save an STL or a 3MF from the Print menu.
Your files stay on your computer. Nothing is uploaded. What leaves the browser is same-origin only, plus the Cloudflare analytics beacon. The modeler stores tinkerclone.bed (the print bed preset and its width, depth, and height in millimeters) and tinkerclone.recovery.v1 (a recovery copy of the model) in localStorage on this site.