A device that allows me to kill any billionaire, world leader, or politician remotely, anywhere in the world, without them being able to stop me.

This is really specific. But I have wanted it for years. A switch for two 3.5 mm sound. Basically plug two inputs into the box, have 1 output and a simple physical switch that would let me flip back and forth.

robot butler that does all my chores

Time machine, please

basically a better newer Kinect for my kids. something that'd let them dance or play or see themselves in the game without a controller

Rocket car that goes through solid matter.

An e-reader running a modern version of Android from an OEM like Google, Samsung, Nokia, etc. I read exclusively using Play Books. I know some exist out there like Onyx Boox, but until they make strides to stay in compliance with the GPL2 they won't get a dime from me.

Holodeck

Iron Man suit.