RawTherapee is a cross-platform RAW image-processing program, released under the GNU General Public License Version 3. It was originally written by Gábor Horváth of Budapest, but has since been taken over by a team of open-source developers from around the world. Rather than being a raster graphics editor such as Photoshop or GIMP, it is specifically aimed at raw photo post-production. And it does it very well - at a minimum, RawTherapee is one of the most powerful raw processing programs available.
Updated on Mar 31 2020
RawTherapee and other open-source projects require access to sample raw files from various camera makes and models in order to support those raw formats correctly. You can help by submitting raw files to RPU: https://raw.pixls.us/