[IshKebab]

I don't think you should really count the operating system by the kernel. You should count it by the API it exposes. That's what really matters.

Under this system Android and ChromeOS wouldn't really be counted as Linux because you can't easily run normal Linux programs on them. Although they may use Linux under the hood, that isn't really visible to user-space programs. Android, and especially ChromeOS could easily switch kernel with no visible effect to apps. The kernel is an implementation detail.

[pjmlp]

Many people that count on Android as Linux, just because of the NDK, usually don't have any idea how little of Linux is actually exposed to developers using the NDK for app development.

Basically any POSIX like kernel with enough support for libc and libc++ would do the job.