Unikernels are essentially the far less interesting cousin of exokernels, in that they nominally preserve the libOS angle but are limited to application deployment under a bare-metal hypervisor.<p>Much of the motivation for microkernel research, too, was for applications to be able to control their workloads at a finer granularity while retaining a full OS environment. Scout and SPIN were such examples. Something as simple as making page replacement and eviction a userland server where each library or application can implement its own policy over the RPC interface, can yield great benefits.