RawTherapee
A powerful cross-platform raw photo processing program
...It’s written primarily in C++ with a GTK+ front-end, providing a high-precision 32-bit floating-point processing engine along with multiple demosaicing algorithms and advanced color-management features. The program supports a very wide range of camera raw formats (via a patched version of dcraw) as well as non-raw formats such as JPEG, TIFF, and PNG. Users can work non-destructively: adjustments are previewed but stored separately (sidecar files) and only applied during export, which allows experimentation without altering originals. The interface includes a file browser, processing queue, editing pane with full-image previews, history stack, and batch export functionality.