  We show that introducing long-range Coulomb interactions immediately lifts
the massive ground state degeneracy induced by geometric frustration for
electrons on quarter-filled triangular lattices in the classical limit.
Important consequences include the stabilization of a stripe-ordered
crystalline (global) ground state, but also the emergence of very many
low-lying metastable states with amorphous "stripe-glass" spatial structures.
Melting of the stripe order thus leads to a frustrated Coulomb liquid at
intermediate temperatures, showing remarkably slow (viscous) dynamics, with
very long relaxation times growing in Arrhenius fashion upon cooling, as
typical of strong glass formers. On shorter time scales, the system falls out
of equilibrium and displays the aging phenomena characteristic of supercooled
liquids above the glass transition. Our results show remarkable similarity with
the recent observations of charge-glass behavior in ultra-clean triangular
organic materials of the $\theta$-(BEDT-TTF)$_2$ family.
