Photivo is a free and open source (GPL3) photo processor. It handles your RAW files as well as your bitmap files (TIFF, JPEG, BMP, PNG and many more) in a non-destructive 16 bit processing pipe with gimp workflow integration and batch mode. Photivo requires GraphicsMagick to be compiled with the configure option "--with-quantum-depth=16": this is enabled by default in the latest GraphicsMagick build script, so if you have problem starting photivo be sure to have the latest version.