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.
