Piranha Alpine Knife

does not get any smaller, one of the few knives made for climbers only, not much other function. Somebody else made a biner knife, but it did not fit on most biners, forget who it was (had plastic casing), but the knife was way too big anyway. This is perfect (unless you are in bear country). Cannot open when on the biner, but Trango gives a little disclosure on their site that it can wiggle open on some biners, so pay attention where you put it. They also do one on the end of a nut tool for $10 more.

little tool. Very light and compact. Designed for climbers. I can't imagine a better one.