For PCs running Microsoft Windows, we recommend:  MicroDicom - MicroDicom - Free DICOM viewer and software

For MAC OS: 

• You can run MicroDicom in Wine - How to install MicroDicom DICOM Viewer on macOS? | MicroDicom DICOM Viewer
• WEASIS (opensource/free version) - Download Weasis DICOM Viewer :: Weasis Documentation
• Horos - Download Horos - Horos Project