It works using either the Mac operating system or dcraw. See - http://en.wikipedia.org/wiki/Dcraw
Its very simple and, if like me, you don't want to spend your time typing in code, it has a nice easy to understand interface and is a stand alone programme.
Its quick, its good and its FREE!
Those who have explored this with regard to m4/3 will know that both Olympus and Panasonic make some "adjustments" to their files in-camera. CA, Distortion etc. There are "lively" discussions about this on forums. Many people criticise the lens construction, of Panasonic in particular, arguing that if software is needed to correct their faults then they can't be that good. In truth the corrections are minor as can be seen using a dcraw conversion. Since this bypasses all the manufacturers tweaks you get to see exactly what the sensor/lens combination can do.
What this does do, in fact, is demonstrate just how good the Panasonic m4/3 sensor is, and also how good the lenses are. There is more CA and noise in a dcraw based conversion, but nowhere near as much as you might expect.
One interesting phenomenon is that if you use a programme like Rawker to convert your files you get a bigger file. In the case of these Olympus E-P2 files 1.2 MB bigger. 34.9 MB becomes 36.1 MB.
In the examples below you can clearly see this.
Olympus E-P2 14-42 Kit Zoom Lens
Olympus E-P2 Lumix 20mm f/1.7 Pancake lens
In general I like Rawker. Its very useful with files that have problematic dynamic ranges. Its default conversion seems to be very low contrast and shadows are lighter and there are less blown highlights. The downside is that more noise is produced in some files, though not all. It also allows me to make the adjustments that I want, rather than those imposed on me by the manufacturers. Its very useful for m4/3. Not so good for my Leicas, which certainly seem to achieve optimum quality via Photoshop.
If you use a Mac and you would like to give it a try, then I would definitely recommend it. If only to get an idea of what your files really look like in the closest version of them to "Authentic Raw"
The bigger file phenomenon applies to images shot with legacy lenses also, as in this shot taken with a Zeiss 21mm f/2.8 Biogon lens fitted to the Olympus E-P2.