ImageOptim - Faster web pages and apps.
Ralpha Image Resizer - High-speed image batch conversion tool
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
JPEGmini - JPEGmini - The Photo Optimization Tool Trusted by Tens of Thousands Image Perfectionists
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.