Scarab Darkroom is a free and easy-to-use RAW file converter which supports cameras from Canon, Nikon, Olympus, Panasonic, Pentax, Samsung, and Sony (the full list is available on the program site).
After a simple installation (no adware to worry about), the program launches with a right-hand sidebar which displays your system's drives and folders. There are no menus here; the idea is that you navigate to a folder containing your RAW images, and a straightforward thumbnail browser helps you to find and view the pictures you need.
That's just the start, of course. The program also has options to rotate or crop your images. An Adjustments provides multiple tweaks (Brightness, Contrast, Recovery, Blacks, Fill Light; Temperature, Tint, Hue, Saturation, Vibrance; Sharpen; Highlights, Midtones, Shadows), as well as being able to save your settings and apply them to other images. And a Metadata tab provides a few details on the image, where possible (Exposure, Aperture, Focal Length, ISO, Flash Used, Date Taken and Camera), and allows you to set an image rating.
And if you're still finding the RAW format just a little too restrictive, then no problem - you can save the image as a JPG or TIFF file.
There are a few gaps in functionality here, in part because this is the free version. There's no noise filtering, for instance - if that's important to you then you'll need to check out the upcoming commercial edition.
Scarab does plenty for a free tool, though, and it's also fast, easy to use and supports a wide range of cameras. If you're currently looking for a good RAW converter then this is a very reasonable place to start.