Magnetic "Micro-robots"

These magnetic particles are manipulated by magnetic fields to open and close their pincers and pick up a glass bead to move it around. The particles lie at the interface between layers of oil and water. A magnetic field perpendicular to the interface causes the particles to form the clumps/"micro-robots" and a magnetic field parallel to the interface causes them to swim. So the next step is obviously to filter different beads from a mixed bag of them. And then, world domination.

Magnetohydrodynamic Drive

Actually, a magnetohydrodynamic (MHD) drive uses some electrohydrodynamics as well. Generally salt water flows though the poles of a magnet while a current is run through the salt water. The interaction of the current and the magnetic field cause a force that pushes the ions. The ions drag the water with them creating a jet and propelling the craft in the opposite direction. Get all that? No? Well you're in luck because there's a picture that explains everything, just replace the plasma with salt water.