Darktable is a totally free Adobe LightRoom alternative RAW photograph editor. It is not only free but opensource but is it an actual LightRoom replacement? It is very similar to LightRoom in appearance. It is somewhat similar controls to LightRoom.
If you are a Adobe LightRoom user for a long time this may not be for you. If you are a new RAW editor but you don’t want the expense of the Adobe product Darktable may be just what you need.