[jradd]

CoreOS' most noteable feature is the fact that it is incredibly light weight and fosters a modular enviornment that (IMO) is less likely to be plagued by dependency hell related issues that you might tolerate from other distros' package management system (Not talking about you Portage, your still coooo).

CoreOS does this by utilizing Linux containers via Docker to easy–bake applications through individual containers of which are explictly isolated from eachother, aiding in the problem of static/dynamic shared libraries causing dependency issues.

Now you can of course utilize all of this on a distro like Debian, and even borrow the best of CoreOS like etcd (for one example).

TL;DR; CoreOS features awesome concepts and services like etcd, and fleet, and more that doesn't mean you cannot do the same with Debian, but it won't be native, and it would not be very light weight out-of-the-box compared to CoreOS.