(OM) theory in diverse dimensions

Open string theories can be decoupled from closed strings and gravity by sc aling to the critical electric field. We propose dual descriptions for the strong coupling limit of these NCOS (Non-Commutative Open String) theories in six or fewer spacetime dimensions. In particular, we conjecture that the 5-dimensional NCOS theory at strong coupling, is a theory of light Open Me mbranes (OM= (sic)), decoupled from gravity, on an M5-brane with a near-cri tical three-form field strength. The relation of (sic) theory to NCOS theor ies resembles that of M-theory to type-II closed string theories. In two di mensions we conjecture that supersymmetric U(n) gauge theory with a unit of electric flux is dual to the NCOS theory with string coupling 1/n. A const ruction based on NS5-branes leads to new theories in six dimensions general ising the little string theory. A web of dualities relates all the above th eories when they are compactified on tori.