Longitudinal wave climber
This was a successful demonstration of a "Longitudinal wave climber" - a vibrating wooden rod on which a "Climber was attached. At the top and bottom of the rod are speakers, modified so that they can directly transmit sound waves to the wooden rod. The top speaker was set to run exactly out of phase with the bottom speaker. This combination (and maybe something else I missed) would cause the "Climber" to move up and down at will. This was brought to the 2009 EuroSpaceward conference by Aage-Raymond Riise (and two assistants) from EAS-ESOC, Germany.