Nomacs is a free, open source image viewer, which supports multiple platforms. Developed by Markus Diem, Stefan Fiel and Florian Kleber
License: Open Source
Nomacs is a lightweight, cross-platform image viewer with basic editing tools, making it ideal for quick viewing and editing. XnView, on the other hand, is more feature-rich with strong organizational and batch processing capabilities, making it better suited for users who need to manage large image collections.