Microsoft and Canonical partner to bring Ubuntu to Windows 10

To clarify, it sounds like what Microsoft has added to Windows 10 is a Linux ABI.

This has been done before with other x86 OSes: FreeBSD has had 32-bit ABI compatibility for at least a decade (https://www.freebsd.org/doc/handbook/linuxemu.html), and the "lx branded zone" for Solaris also has 64-bit support (https://docs.oracle.com/cd/E19455-01/817-1592/gchhy/index.ht...).

It looks like Ubuntu was the first to package some Linux binaries for Windows. I guess that's useful?

Linux ABI support was introduced in FreeBSD 2.1 released in 1995, 20 years ago.