Exokernel vs. Unikernel — What's the Difference?

Exokernel is an operating system kernel developed by the MIT Parallel and Distributed Operating Systems group, and also a class of similar operating systems. Operating systems generally present hardware resources to applications through high-level abstractions such as (virtual) file systems.

A unikernel is a specialised, single address space machine image constructed by using library operating systems. A developer selects, from a modular stack, the minimal set of libraries which correspond to the OS constructs required for the application to run.

(computing) A very low-level kernel that avoids abstractions.

(operating systems) A specialised, fixed-purpose machine image which can run directly on hardware or a hypervisor without an operating system such as Linux.