The folks at Festo, who work on pneumatic and electrical automation technology, seem to have a lot of spare time on their hands as they can ply their trade on various fun projects like Air Ray. From their product page here is a little snippet of what makes it work:
Air_ray, modelled on the manta ray, is a remote-controlled hybrid construction consisting of a helium-filled ballonet and a beating wing drive. Its light design makes it possible for it to “swim” in the sea of air, boosted by helium, in a similar way to the manta ray in water.
I could really imagine having a couple of these gliding in a large conference hall right above my head. Gracefully swimming here and there. Further info can be found here about Festo's Air Ray - [Link].
YouTube - [Link]