Free RAW processors include:
Linux, Windows, Mac, BSD...
'stable' version is 2.4.1 (now considered obsolete); the beta versions of 3.0 are pretty solid now. For Windows and Linux, Mac in the works.
v3 - for Windows, keep an eye on this thread:
v3 for Linux:
v3 for Mac:
Roll (compile) you own:
Darktable is free, too (Windows and Linux; Mac port currently not maintained).
To see it in action:
Photivo is multi-platfrom (Windows, Linux, Mac) and free. Branched from PerfectRaw (now unmaintained), I think.
Works on Linux only: