There's a lovely surface and curve editor called PolyCAD by a guy named Marcus Bole on polycad.co.uk, it's a parametric ship modeler too. Not open but free, he requires registration, but it's the most intuitive curve/surface editor there is, IMO. Manual or numeric editing, plain English file format, so you can format an x,y,z list, declare it a mesh or a spline surface or curves or polylines, give the text file a .geo attachment, open it in PolyCAD and transfer as .dxf or .igs, even some ACIS .sat. Has zebra visual smoothing too. Only Windows, it's a small price to pay because it's awesome for what you want to do. Your youtube vid looks promising too, microelly2. Numerical editing?