Darktable takes photos in the Raw format captured by your camera’s sensor and makes non-destructive edits to them. It works as a database, with a series of modules that perform operations on records (photos). For example, the Collect module enables
you to search for images by tag, rating, and other metadata.
Other modules enable you to crop and rotate images, perform
curve adjustments to change a picture’s tonality, and recover blown out highlights. Several modules add artistic effects: watermarks, frames, and vignettes, and you can soften images, add grain and simulate human low light vision.
Darktable’s modular, open‑source nature means it’s constantly evolving. Check it out if you miss Aperture’s processing tools and don’t want to spend on Lightroom.