[NativeSon]

As with the "ion drive", propulsion is achieved by "pushing" a wave or particle. Avoiding the whole, wave-particle duality, the cumulative thrust of such a small force (say exhaling) would amount to significant momentum over time.

In a zero - or more princely low gravity - environment, trivial forces can become substantial. I don't know much about this "EM Drive" but seems to fit that. Now how about spinning up a gyroscope in space and using that for a drive system...

[Telepathic Intruder]

A gyroscope produces only angular momentum, not thrust. But even then, all motion is conserved. To spin something, you need to apply an opposite force. If I spin a top, I would have to apply a force that would make me spin the other direction if I couldn’t use the friction of the ground against my shoes to stop me. Conservation of momentum means that for every object set in motion, it is balanced by another object, so that the net result amounts to zero.