Rawstudio
I've been puzzling over how to go about manipulating the NEF RAW images my camera produces. Obviously, it is better in principle to shoot in RAW than in JPEG, but the tools for editing RAW files under Linux do not seem to be very far along. For example, The Gimp doesn't natively support them. But that isn't to say there are no tools. Rawstudio provides pretty solid toolbox of basic manipulations. I can finally fix up the colors in some of my favorite shots.
Now, if only I had some good way of doing demosaicing, I'd be all set.
