Geeqie is a lightweight image viewer. It was forked from GQview. The development is focused on features for photo collection maintenance: raw format, Exif/IPTC/XMP metadata and integration with programs like UFraw, ImageMagick, Gimp, gPhoto or ExifTo The current development and project can be found on http://www.geeqie.org/. The sourceforge page will be deleted soon.
gPhoto is a program and library framework that lets users download pictures from their digital cameras. The libgphoto2 library gives you access to hundreds of models of digital cameras on several platforms. GIT repo and Issue tracker lives at https://github.com/gphoto/ these days.
nomacs is a fast and small image viewer
nomacs is a free image viewer for windows, linux, and mac systems, which is licensed under the GNU Public License v3. nomacs is small, fast and able to handle the most common image formats including RAW images. NOTE: nomacs has moved: http://download.nomacs.org
The continued maintenance of Michael Gundlach's CatBlock
After the creator of AdBlock, Michael Gundlach, retired official support of the CatBlock project, and made it Open-Source under the GNU GPLv3, two people decided to continue maintenance, albeit unofficially. This is that project.
Piwigo is a photo gallery software for the web. It comes with powerful features for publishing your photos and smart browsing capabilities such as categories, tags, or chronology. Extensions make Piwigo easily customizable.
xCHM is a cross-platform GPL frontend for CHMLIB (http://www.jedrea.com/chmlib/) written with the wxWidgets framework.
Mig is designed to be a simple but flexible program that enables users to manage online photo galleries.
gtkalbum will be a GTK application written in C for showing and organising photo albums from digital cameras. It will allow some basic funcions like rotating image. It will show EXIF information and use 160x120 previews directly from JFIF (jpeg) images.