Lamentations of the Flame Princess points out that, in a world where magic items can be made, not all of them will be made to benefit the adventuring professions. Since upwards of 99% of people won't fall into that category, in fact, it seems like most magic items will not have direct applicability to exploration or combat. I do like the idea, however, of something that might be pressed into adventuring service with a little cleverness, so I came up with the following:
The Abacus of Xallim.
|Looks something like this, but more awesome.|
It is widely believed that the wizard Xallim bound the spirit of an obsessive savant into the abacus. Some say he bound it into the very wood of the frame, while others speculate its powers have something to do with the strange engraving on the side: an imp, viewed through a four-paneled window, handing a fruit of some sort to a small, flightless bird. Regardless, it appears as a well-made example of its type, capable of counting up to 9,999,999,999. Four red beads on a rod running perpendicular to the rest, on the top of the frame, count the number of daily charges it has left to use. These slide up and cannot be pulled down until the charges reset.
To operate the abacus, the user must say, in any language known to mortal men, the following: "The task has come to you, servant of Xallim, to tally and report the number of [X] that lies [or stands, etc.] before you." Then, placing fingers on the bead, the user will feel an urge to slide the beads back and forth for a frantic period of 10 - 15 seconds. Doing so will reveal the number. If secrecy is desired, the command may be whispered, but it still must be physically uttered.
Without expending any charges, it can instantly size up the number of objects of a type in plain sight.
For one charge, it can discern between real and fake, or pure and adulterated, coins, by counting how many apparent and real numbers of an item are under consideration. The beads will flip back and forth between the two tallies; although it may confuse the outside observer, the user will be able to read the values instantaneously.
For two charges, the abacus can determine if any hidden/secret doors or traps (and how many) exist within viewing range.
By using up all remaining charges for the day, it can determine, as the answer to a yes-or-no question, if an item is magical or legendary. A count of 1 means yes, 0 means no.
While all of the daily charges are exhausted, even the chargeless function ceases. It still works as a regular abacus, however.
There is a 3% chance per use that the user will become afflicted with the compulsion to remain obsessively clean and orderly, which would preclude most adventuring activities. This effect will remain until someone casts a Remove Curse on the user.