what was this wheeled device?

just got back from the soltice parade in fremont

there was this device that even the bike shop on the parade
route had never seen but thought it was cool too but didn't
know what it was called

but it consisted purely of a seasaw mounted on an axle and
two wheels the people on it were able to move backward and
forward and spin in place

utterly cool and simple

but after searching for 30 min on the internet, nothing
comes up any ideas what it is called, plans???