The versatility and quality of RAW format images comes at a cost of convenience. The standard JPEG is viewable by almost everything these days, but support for higher quality images in RAW format like JPEG2000 or NEF is limited. Adobe’s Camera RAW can handle most of these formats, but with some formats things can get complicated or require tricking the software into working.
For this reason, alternative software is always handy to have accessible in your toolbox.
UFRaw is one of these alternatives. It is a project in active development but still has some basics to complete. It’s also a bit more convoluted of an install on a Windows PC. None the less, this will be something to keep an eye on if RAW images are a part of your daily workflow.
RawTherapee is another alternative but this one comes off as a bit more polished than UFRaw. RawTherapee is also in active development and packages much more nicely for Windows. Check out if your camera is supported and major features. This seems to be a great alternative to commercial or proprietary camera RAW software.
IrFanView is another option that with a plug-in works to allow viewing a lot of different formats including Nikon’s NEF and a good deal of others. There are also many more plug-ins to expand this program to work for you.