Minkowski spacetime (which describes empty space with no cosmological constant) Milne model (which is a model developed by E. A. Milne describing an empty universe which has no curvature) Schwarzschild vacuum (which describes the spacetime geometry around a spherical mass), Kerr vacuum (which describes the geometry around a rotating object), Taub-NUT vacuum (a famous counterexample describing the exterior gravitational field of an isolated object with strange properties), Kerns–Wild vacuum (Robert M. Kerns and Walter J. Wild 1982) (a Schwarzschild object immersed in an ambient "almost uniform" gravitational field), double Kerr vacuum (two Kerr objects sharing the same axis of rotation, but held apart by unphysical zero active mass "cables" going out to suspension points infinitely removed), Khan–Penrose vacuum (K. A. Khan and Roger Penrose 1971) (a simple colliding plane wave model), Oszváth–Schücking vacuum (the circularly polarized sinusoidal gravitational wave, another famous counterexample). Kasner metric (An anisotropic solution, used to study gravitational chaos in three or more dimensions).