MRIcron is a cross-platform NIfTI format image viewer. It can load multiple layers of images, generate volume renderings and draw volumes of interest. It also provides dcm2nii for converting DICOM images to NIfTI format and NPM for statistics. MRIcroGL is a variant of MRIcron that uses OpenGL for very fast rendering, but requires a modern NVidia or ATI graphics card.