support for color-managed workflow: user-defined input, work and output profiles, soft-proofing, etc. ability to load and edit images of arbitrary size, thanks to the underlying rendering engine based on the VIPS library architecture based on Plugins: implement quickly new tools as separate modules that load at runtime 8-bit and 16-bits support, including 32-bits and 64-bits floating point precision, selectable at runtime and on a per-image basis support for fully non-destructive, layer-based photo editing workflow with realtime preview of the final image
color-correction options: black and white conversion, contrast/brightness adjustment, channel inversion, custom tones curves, hue/saturation adjustment, channel inversion, horizontal/vertical/radial gradient. color-managed processing in floating-point support colorspace conversions based on ICC profiles (partly implemented) support for RAW, JPEG, TIFF plus EXIF data and ICC profiles
Note: You can find a PhotoFlow tutorial here and the Install instructions (for various OS) here. The program interface has a similar interface with GIMP or Photoshop by organizing the editing into layers, layer groups, and masks. The software is still in a developing stage, allowing you to open an image and apply basic editing filters using non-destructive adjustment layers. It is similar to Darktable or RawTherapee, and it already integrates a large number of filters from GMIC.
PhotoFlow is a free, open-source non-destructive photo retouching program that provides a complete RAW image editing workflow.