A harmonically driven cavity QED system consisting of two cavities and a two-level qubit is shown to enable the generation of a vast class of maximally entangled states suitable for measurements with a Heisenberg-limit precision. As one of its modalities, this system can serve as a quantum beam splitter, converting an |N〉 ⊗ |0〉 input into a maximally entangled N00N state (|N〉 ⊗ |0〉 + |0〉 ⊗ |N〉)/ at its output. A network of such quantum beam splitters is shown to provide a source of multimode N00N-type entanglement.