Well, I've just just had a barn cat move in after years of being without one and have noticed much less rodent activity down there...but I am buying cat food again, which I didn't have to do for the weasel. A cat is not a tool though, so I would either vote for my bow saw or the splitting maul for firewood utility. (Can't run a chainsaw) In the summer, it would be either my little anti- vibration hammer, fencing tool, the clamshell fence post hole digger or my stainless steel tree planting shovel. Those are small tools, but the big FEL on the tractor gets used all year long, I haul firewood in it, use it to encourage leaning trees to lie down, haul round bales, haul manure and compost, plow snow, move heavy objects, hang beef and lambs at slaughter time, dig a bit of dirt, tighten barb wire, move mini bags of grain, haul thistles.
I vote for the FEL as the most useful tool on the farm!