Background info: https://www.darktable.org/2015/07/why-d ... ows-build/
Unofficial Windows builds: http://www.partha.com/ (Not Portable) (other good stuff on there too)
This program is somewhat comparable to RawTherapee & Photivo with its comprehensive feature list, modular workflow and dark interface.
The authors wrote:darktable is an open source photography workflow application and RAW developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them.