Darktable - darktable is an open source photography workflow application and raw developer.
Ralpha Image Resizer - High-speed image batch conversion tool
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
OnlineImageResize.com - Free online image resizer. Resize your image fast and easy. Image resizer online!
RawTherapee - RawTherapee is a free RAW converter and digital photo processing software.