  We propose an extension of General Relativity (GR) based on a space-time
foliation by three-dimensional space-like hypersurfaces labeled by the Khronon
scalar field $\tau$. We show that this theory (i) leads to modified Newtonian
dynamics (MOND) at galactic scales for stationary systems; (ii) recovers GR
plus a cosmological constant in the strong field regime; (iii) is in agreement
with the standard cosmological model and the observed cosmic microwave
background anisotropies at linear cosmological scales, where the theory reduces
to a subset of the generalized dark matter (GDM) model. We compute the second
order action on a Minkowski background and show that it contains the usual
tensor modes of GR and a scalar degree of freedom with dispersion relation
$\omega=0$. We find that the deconstrained Hamiltonian is bounded from below
for wavenumbers larger than $\sim 10^{-31}\,\text{eV}$ and unbounded for
smaller wavenumbers.
