Could someone with more knowledge about the subject explain why launchd was never taken up outside of OS X? I'm not an admin by any stretch of the imagination, but it seems to fit the bill fairly well, and I've always wondered why it has not been ported elsewhere.
Partly because launchd didn't have a sensible Open Source license, and partly for the same reason systemd doesn't run on non-Linux kernels: it's designed for its target OS, and makes use of that OS's native functionality to the point that porting would become decidedly non-trivial.
systemd took heavy inspiration from launchd and other sources, but provides extensive functionality that launchd does not.
Licensing issues at the time. That's what Upstart was initially meant to be, actually: a native launchd clone. If it wasn't for the Apple Public Source License that launchd was under back in 2006, Ubuntu would have probably been using it right now.
