MirageOS is a very interesting project, as it's an operating system library for building unikernels for secure or high-performance applications geared towards networking, the cloud, mobile platforms, and more. These unikernels can be compiled on GNU/Linux and other Unix-like operating systems, and can also run on the KVM hypervisor or Xen for virtualization.
To achieve this, MirageOS uses OCaml, a language with libraries that provide functionalities for networking, storage, and other system-supported features. The latest version, MirageOS 3.0 , was released in February 2017. Those interested can download it and find more information about the project at mirage.io.
For those unfamiliar with unikernels , they are specially designed structures that use only the minimum number of operating system libraries necessary to run a given application. This eliminates the need to virtualize the entire operating system and improves overall performance. The application code, the libraries, and this general-purpose unikernel are all compiled to run directly on a hypervisor or hardware without requiring an operating system to intervene.
And it's not just a matter of performance (requiring only 4% of the size of a traditional OS, and with optimized drivers), it also improves security by reducing the amount of code deployed to run the application, thus leaving less room for attackers. Not to mention its versatility and importance for modern applications. That's why there are more and more projects like MirageOS, OSV, Runtime.js, IncludeOS, HermitCore, HaLVM, Clive, Grafene, ClickOS, and others.