MirageOS is a library operating system that constructs unikernels for secure, high-performance network applications across a variety of cloud computing and mobile platforms. Code can be developed on a normal OS such as Linux or MacOS X, and then compiled into a fully-standalone, specialised unikernel that runs under the Xen hypervisor.
Since Xen powers most public cloud computing infrastructure such as Amazon EC2 or Rackspace, this lets your servers run more cheaply, securely and with finer control than with a full software stack.
MirageOS uses the OCaml language, with libraries that provide networking, storage and concurrency support that work under Unix during development, but become operating system drivers when being compiled for production deployment. The framework is fully event-driven, with no support for preemptive threading.