Some "non-" or "extra-functional" features, such as reliability, security, and tracing, defy modularization mechanisms in programming languages. With distributed, heterogeneous (DH) systems, these features induce complex implementations which crosscut different languages, OSs, and hardware platforms, while still needing to share data and events. The DADO approach helps program crosscuting features by improving DH middleware. A DADO service comprises pairs of adaplets which are explicitly modeled in IDL. DADO supports flexible and type-checked interactions (using generated stubs and skeletons) between adaplets and between objects and adaptlets. Adaptlets can be attached at run-time to an application object.