The free view/measure/print/markup application for CAD data - Autodesk Design Review - supports not only DWF/DWFx files (2D and 3D) but also many other CAD and raster image formats.
The enhanced Open dialog now offers a list of directly supported extensions (file types). Design Review supports the files: DWG, DXF, PDF, BMP, CAL, CALS, CG4, FLC, FLI, GIF, GP4, JPG, JPEG, JPE, JFIF, MIL, PCX, PCT, PICT, PNG, RLC, RST, TGA, TIF, TIFF. So you can use it as a free viewer for these data formats.
For support of DWG and DXF files you need to install the Autodesk DWG TrueView software.