If you could have any sci-fi gadget or technology, what would you choose?

I choose: a Culture knife missile.

*"The door burst open, slamming against the mud wall. Sma flinched. The two black-cloaked men filled the doorway. She could smell them. One strode in towards her, sword out, rope in the other hand, not noticing the drone at her side.

'Excuse me,' said Skaffen-Amtiskaw.

The man glanced at the machine, without breaking stride.
Then he wasn't there anymore, and dust filled the room, and Sma's ears were ringing, and pieces of mud and paper were falling from the ceiling and fluttering through the air, and there was a large hole straight through the wall into the next room, across from where Skaffen-Amtiskaw - seemingly defying the law of concerning action/reaction . Hovered in exactly the same place as before. A woman shrieked hysterically in the room through the hole, where what was left of the man was embedded in the wall above her bed, his blood spattered copiously over ceiling, floor, walls, bed and her.

The second man whirled into the room, discharging a long gun point-blank at the drone; the bullet became a flat coin of metal a centimetre in front of the machine's snout, and clunked to the floor. The man unsheathed and swung his sword in one flashing movement, scything at the drone through the dust and smoke. The blade broke cleanly on a bump of red-coloured field just above the machine's casing, the the man was lifted of his feet.

The man trashed wildly in the centre of the room for a second, then he was a blur through the air above her. There was another colossal pulse of sound, and a ragged aperture appeared in the wall over her head, beside the window looking out to the square.

One of the warriors roared, brandishing his sword and lunging towards the door of the inn.

He managed two steps. He was still roaring when the knife missile flicked past him, field outstretched. It separated his neck from his shoulders; the roar turned to a sound like the wind, bubbling thickly through the exposed wind-pipe as his body crashed to the dust.

Faster - and turning more tightly - than any bird or insect, the knife missile made an almost invisibly quick circle round most of the riders, producing an odd stuttering noise.

Seven of the riders - five standing, two still mounted - collapsed into the dust, in fourteen separate pieces.

In the square, both of the inn-keeper's daughters slipped to the ground from the mounts they had been tied to, their bonds slashed in the same cut that killed all seven men.

One man dropped his sword and started to run. The knife missile plunged straight through him. It curved like a red light shining on a hook, and slashed across the necks of the last two dismounted riders, felling both. The mount of the final rider was rearing up in front of the missile, its fangs bared, forelegs lashing, claws exposed. The device went through its neck and straight into the face of the rider.

The knife missile spun slowly about, seemingly reviewing its few seconds' work, then it started to float back towards the window."*