I had no idea MirageOS existed ("MirageOS is a library operating system that constructs unikernels for secure, high-performance network applications").
Fortunately the university of Cambridge has a decent explanation of what it is and why should I care:
"The cloud has so far mostly been used to consolidate existing operating systems and manage them more conveniently. The interface between guest kernels, applications and VMs are all managed very differently, leading to serious inefficiencies, unreliability and insecurity. Mirage OS revisits the library OS concept (built here as Nemesis in the late '90s), and narrows the gap between safe, high-level programming, and low-level systems construction.
Applications are written in high-level OCaml and compiled directly into microkernels that run on the Xen hypervisor. By treating the hypervisor as a stable hardware platform, we can focus on high-performance protocol implementations without worrying about having to support the thousands of device drivers found in a traditional OS. "