Only X and Y (and Alpha Sapphire if that counts as older) but Pokemon can be transferred from Black and White 2 with Pokemon Bank, so you can kind of indirectly trade Pokemon over like that. But if you don't have PokeBank, the only games Omega Ruby can directly communicate with are Alpha Sapphire, X, and Y.
Any game since generation 3, technically, using poketransfer, but in that you must have reached a certain point, and the Pokemon can't hold items. You can also directly trade from X, Y, and AS.
