Fabricator
Build a topographic model from stacked chipboard or cardboard. Choose a parametric form (or drop in your own STL/OBJ/PLY, raycast into a terrain) and your sheet thickness, and it traces every level with marching squares and stacks them into a stepped 3D preview of the model you'll cut.
Runs entirely in your browser — nothing is uploaded. Export a numbered, nested SVG cut sheet (each layer shows the next one scored in blue so stacking is foolproof) and a flat contour map — both sized in real millimetres. Pairs with the Topography Builder.