Horos - A free, open source 64-bit DICOM medical image viewer
miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
Weasis - Weasis is a multipurpose standalone and web-based DICOM viewer.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
3D Slicer - Slicer is a community platform created for the purpose of subject specific image analysis and...
Paint XP for Windows 7 - Standalone old MS Paint program that allows you to get your old XP Paint interface in Windows 7.