darktable

darktable handles the full RAW pipeline — import, cull, tag, develop, export — with a genuinely powerful scene-referred processing engine. Modules like filmic and color balance rgb give you more low-level control than Lightroom does, and it never touches your originals. OpenCL acceleration makes it fast on a decent GPU.

The flip side of that control is a brutal learning curve: expect to spend a weekend on documentation before your edits look better than Lightroom’s auto button. Its catalog/library features are also weaker than Lightroom’s, and there’s no cloud sync story at all. Migrating existing Lightroom edits is essentially a fresh start.