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

ExifTool is a free and open-source software program for reading, writing, and manipulating image, audio, video, and PDF metadata.

Iconfinder is a search engine for icons.

ImageOptim makes images load faster. Removes bloated metadata. Saves disk space & bandwidth by compressing images without losing quality.

F-Spot is an unmaintained image organizer, designed to provide personal photo management for the GNOME desktop environment.

JPEGmini is a photo optimization software.