dxf2svg2kicad is a DXF to SVG to KICAD_PCB converter webapp that runs purely on the client side.
You can read some background info in the release announcement and another relevant thread on the kicad-users mailing list.
- AutoCAD DXF File Format Summary
- DXF Reference for various versions of AutoCAD by Autodesk
- Mad props to Rob Gilliom for making me realize that it's quite easy to parse DXF files.