Okular - Okular is a universal document viewer based developed by KDE.
Saint Paint Studio - Saint Paint - The Essential Image Editor
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Stet.io - Stet.io is a high-quality pixel management platform that allows editing the pictures with online commands or multiple options with real-time effects or filters.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
ImageForge - - ImageForge Standard Freeware Edition: