Please note anything that does not fall under a FLOSS license!
MeshLab a mesh processing tool to convert, clean, inspect, repair 3D meshes. Many supported 3D formats (STL, 3DS, OBJ, Collada, VRML, X3D, PLY etc)
LibreCAD a 2-D CAD program, is a port of Qcad (Free Community Version) to Qt4. It should be very familiar to anyone who has used Qcad, and easy to learn if you've never used it before. DXF file format. Versions available for Linux, Mac, and Windows.