AMIDE is described as 'completely free tool for viewing, analyzing, and registering volumetric medical imaging data sets such as SPECT/PET/CT. Renderization in 3D and much more' and is an app. There are more than 10 alternatives to AMIDE for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and iPhone. The best alternative is InVesalius 3, which is both free and Open Source. Other great apps like AMIDE are MicroDicom, Horos, 3D Slicer and Miele-LXIV.
Miele-LXIV is a DICOM workstation, viewer and more. The project started in November 2014 as a fork of the popular open source 32-bit project OsiriX, but it has been modified to become a 64-bit application and to remove many of the limitations of the 32-bit version.
postDICOM is a cloud-based DICOM Viewer and clinical documents viewer. You can upload DICOM files and clinical documents using web browsers. You can upload and view your DICOM files from PCs(Windows, MacOS, Linux), tablets and phones(IOS and Android).