is a sort of 'antigravity' device.
It can be constructed from a number of different materials, but typically it is made from aluminum foil and small sticks; the whole thing has to be really lightweight, and frequently has a triangular shape.
To make the 'antigravity' work, you connect the lifter to high voltage source; and it takes off, often with a great deal of corona and a smell of ozone. Oh yeah, and sometimes it catches fire.
Anyway, it doesn't seem to be real antigravity. It's not completely understood how it works, but it looks like it is something to do with electric currents that travel through the air which causes air currents that pushes the lifter into the air. It does also work in a vacuum, but not nearly so well- it looks like the ions give lift more directly in vacuum.