RawTherapee is a free, open-source, cross-platform photo development program focused on working with raw camera image files (and other high-quality formats). It works on Windows, macOS and Linux.
If you shoot raw images and want serious control over how they are developed — adjusting demosaicing, colour spaces, highlight/shadow recovery, sharpening, noise reduction, output bit-depth, etc. — RawTherapee offers very advanced tools without cost. For photographers who don’t want to pay for a subscription or want full access to internals, it’s appealing. For example, reviews note that “if you’re willing to spend a few hours getting to grips with how it works… it could be one of the best free photo editing programs”
You import raw files (or JPEG/TIFF) into its file browser, apply adjustments in the editor module (non-destructively, via sidecar files). It uses a high-precision 32-bit floating-point engine internally. You can choose from multiple demosaicing algorithms (AMaZE, IGV, LMMSE etc) for precise control.
