They're part of the same group of systems programmers aligned in their values of how to build software. Andreas was featured [0] at our conference that Andrew Kelley gave a talk for. (Though I believe they were friends before this.)

Someone mentioned BoksOS. That one is explicitly using Zig and made a conference demo [1] too.

[0] https://media.handmade-seattle.com/serenityos

[1] https://media.handmade-seattle.com/boksos