[moby_click]

1) According to the source article, a unikernel is a kind of library OS and I think you hit the right spot with

2) specialization. AFAIK the the concept of a library OS is from a time when single purpose computing was not on the agenda. We could argue a lot about the different ways of multiplexing and isolating different workloads and how maybe privilege levels were meant to solve the same problem as hardware virtualization but the spirit of unikernels (and library OSs) is to use language and program against an API that specializes to whatever ABI your target happens to be. The name unikernel is used more in the context of specialized applications in the sense of what a UNIX process is supposed to be (do one thing) but I'd say the important aspect is still the use of language technology which then enables specialized code.

I'm not too familiar with OSv but I think the goal is to provide a runtime for off the shelf java applications. It should be possible to fuse an application with just the needed parts of libc and drivers, though.