PhotoQt
PhotoQt is a free and open source multiplatform, fast and simple, yet powerful and highly configurable image viewer
Nomacs
Nomacs – free and open source multiple platforms fast image viewer with additional editing functionality
Phototonic
Phototonic – free and open source software for viewing and organizing images with simple editing functions for Linux
qView
qView – free and open source cross-platform full-featured minimalistic image viewer
Gwenview
Gwenview – free and open source software for viewing images with simple editing features
Eye of GNOME
Eye of GNOME – free and open source Gnome image viewer for Linux