[from the original at: http://blog.zhenzhang.me/2015/10/26/halvm-intro.html]
Overview of Unikernel Development
Unikernel is also called Library OS. As its name spells, it exists in form of libraries to support the production code. You can selectively compile a minimal set of components you need and run the image on hardware or hypervisor.
And several characteristics make it rather suitable for cloud service. However, it is never the traditional user-faced OS.