We describe the design of an application platform able to run distributed real-time and multimedia applications alongside conventional UNIX programs, The platform is embedded in a microkernel/PC environment and supported by an ATM-based, QoS-driven communications stack, In particular, me focus on resource-management aspects of the design and deal with CPU scheduling, network resource-management and memory-management issues. An architecture is presented that guarantees QoS levels of both communications and processing with varying degrees of commitment as specified by user-level QoS parameters. The architecture uses admission tests to determine whether or not new. activities can be accepted and includes modules to translate user-level QoS parameters into representations usable by the scheduling, network, and memory-management subsystems.