Cyclobutane (larger view)
Cyclobutane (larger view)
(How to manipulate JSmol structures)
The fourth carbon in cyclobutane is ~25o out of the plane of the other three carbon atoms thereby relieving some of the the C-H bond eclipsing. (The feet of four-legged stools do not have to lie in a plane.) Place three carbon atoms in a plane. View down a C-C bond and convince yourself that C-H bond eclipsing is reduced.