OTI lounge chair all metabars are straight building a doubly ruled surface, I used 2 of them to build the perfect economic chair.
OTI sidetable
Hyperbolic paraboloid
The hyperbolic paraboloid is a doubly ruled surface: it contains two families of mutually skew lines. The lines in each family are parallel to a common plane, but not to each other. Hence the hyperbolic paraboloid is a conoid.