3D Slicer

3D Slicer is a free, open-source application specializing in medical image visualization and analysis. It reads DICOM files, performs interactive segmentation, and handles rigid/non-rigid registration. Additional features include volume rendering, 4D image viewing, screen capture mode, and extensibility via plugins. This makes it particularly useful as an MRI viewer and for a wide range of image processing tasks in medical research and clinical practice.