A head-mounted display system is provided, including a head-mounted display configured to display one or more virtual objects in a physical environment. The head-mounted display system may further include a processor configured to receive a three-dimensional push notification at an application program via an application program interface (API) of one or more APIs included in a volumetric operating system. The three-dimensional push notification may indicate a first location in the physical environment of an application program virtual object included in the one or more virtual objects. The application program virtual object may be associated with the application program. The processor may generate a three-dimensional push notification virtual object based on the three-dimensional push notification. The processor may output the three-dimensional push notification virtual object for display on the head-mounted display at a second location relative to the first location in the physical environment.