I don’t yet have a multi-spectral capable camera, only infrared, but I plan on getting one at some point in the future. See the diglloyd Guide to Digital Infrared Photography for more on infrared and camera conversions, and also Infrared Cameras Compared.
A multi-spectral camera responds to ultraviolet, visible light and infrared. Most digital sensors are responsive to all these frequency bands, but a stock (unmodified) camera includes sensor glass over the sensor which blocks all but visible light. It is the removal/replacement of this sensor cover glass which allows the sensor to “see” all wavelengths from ultraviolet to infrared. Response in the UV and IR ranges will vary with the sensor of course. Fujifilm sells their Fujifilm IS Pro DSLR as a multi-spectral camera (see Feb 11 comments).
With the advent of the Coastal Optics 60mm f/4 UV-VIS-IR APO Macro, multi-spectral photography becomes a lot more practical, since no focus shift occurs due to wavelength, allowing images from different spectral bands to be layered together with highly-accurate alignment.