[Rochus]

Neither the whole L4 line of work, which fundamentally rely on synchronous, rendezvous-style IPC as their primary kernel-level communication primitive; the transition to synchronous IPC together with the specific way it was designed was absolutely central to the dramatic performance improvements of L4 over first-generation microkernels like Mach. QNX independently pioneered many of the concepts that define successful microkernels.