Creallo Atlas supports STEP, IGES, STL, OBJ, 3MF and other formats on macOS, Linux and Windows. The free desktop application is designed for inspecting and measuring models rather than editing them.
The company says opening files, measuring distances, section views, thickness checks and mesh diagnosis work without signing in or uploading. Optional sharing and automatic repair features require an account.
That makes it a useful complement to Plasticity and Bambu Studio. Try opening a known-good STEP and a troublesome STL, then compare dimensions and mesh warnings.
Action: install the Mac build and run a ten-minute inspection test on two existing files.