Blender (free, open-source 3D suite) can import ArtCAM .rlf files as heightmaps. You write a script or use the “Images as Planes” method: convert the .rlf to a PNG (using a small tool like rlf2png ) and then displace a mesh.
ESTLcam is a tiny, free Windows utility originally designed for STL files, but it can also open files (ArtCAM reliefs). It renders the surface as a shaded 3D model. artcam file viewer
Vectric’s flagship software (Aspire and VCarve) can natively ArtCAM .art and .rlf files. While not a “viewer” per se, the import process opens the file as an editable model. Blender (free, open-source 3D suite) can import ArtCAM