The latest edition of the (some might think mythical) C’T Digital Photography magazine details an open source RAW converter called Photivo.
I decided to give it a try and it seems really powerful. The most powerful open source RAW converter I’ve come across. It’s not the most intuitive piece of software and there is no manual to speak of so it might not be suited to RAW conversion beginners. It does have an awful lot of image parameters that can be tweaked; from common parameters such as exposure to multiple sharpening methods, black and white conversion, vignetting, graduated filters etc etc. A new experimental version also has a spot adjustment tool too. At least with it being non-destructive you can play with the settings as much as you like with no damage being done to your RAW files!
For any GIMP users, it also allows images to be exported directly to GIMP.
A few years back the best RAW converter was a free one, I used it exclusively, then the authors were bought out by Adobe. I’m not sure whether they wanted their talents or they feared the competition. Since then Adobe have developed Camera Raw which is arguably the best RAW converter; available with Photoshop, incorporated into Lightroom or (in simplified form) with Photoshop Elements.
If you need a RAW converter don’t be put off by the fact that this one is free – give it a try and see if it suits your needs.