XnView MP is the enhanced version of XnView Classic. It is a powerful cross-platform media browser, viewer and converter.

gThumb is an image viewer and organizer with a couple of limited options to also edit images.

digiKam is a free and open-source image organizer and tag editor written in C++ utilizing the KDE Platform.

Piwigo is photo gallery software for the web, built by an active community of users and developers.