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???