Here are some random ideas off the top of my head. No idea if any of them are useful.
-A brass sphere that spins at a constant rate of one revolution every thirteen seconds. It requires a full tonne of pressure to stop it spinning, but once you have applied that pressure it can be held in place by hand with no difficulties. Once it is free of all constraints its slowly starts to spin again.
-A hololithic plate that can record and playback the dreams of whoever wears an ornate piece of crystal jewelery.
-A gunsight that highlights the targets central nervous system and locks on to the greatest concentration of neural tissue.
-A 10-bolt clip (that only contains three bolt shells). When fired, the bolt shells break apart into small, semi-sentient mechanical insects that slip though cracks in armour and walls, burrow into the flesh of the targets THEN detonate.
-A pair of perfectly clear wine glasses that turn dark when poison is detected within them.
-Five fifty centimetre long platinum rods. When one detects body heat, the others warm up to the same temperature. Only the presence of a living creature activates this ability.
-A wide, yet thin, table that performs all the functions of a powerful data loom.
-A mundane sword with a cutting edge that is fractal in nature, being infinitely long and sharp.
-A set of playing pieces from a game not unlike regicide, that can be set up on a playing field and can move themselves, providing a stimulating opponent for any player, even one who has never played the game before.