As you can see from this screenshot, it looks just like the real thing:
Mihai explained more in his blog post:
A side effect is that I now have a self-contained Reader installation that I'll be able to refer to years from now, when my son asks me how I spent my mid-20s. It also satisfies my own nostalgia kicks, like knowing what my first read item was. In theory I could also use this approach to build a proxy that exposes Reader's API backed by (say) NewsBlur's, and thus keep using the Reader UI to read current feeds. Beyond the technical issues (e.g. impedance mismatches, since NewsBlur doesn't store read or starred state as tags, or has per item tags in general) that seems like an overly backwards-facing option. NewsBlur has its own distinguishing features (e.g. training and "focus" mode)2, and forcing it into a semi-functional Reader UI would result in something that is worse than either product.
Zombie Reader can be downloaded from Mihai's website, readerisdead.com.
Just to be clear, it cannot be used to browse any current news reader service, and that is probably a good thing. As much as I liked the Google Reader service, I have to admit that the website design needed work. It was not the best tool for reading content, and the overall design needed a little polish. I can only recall Google making a single change to the Google Reader design, and that was when they uglified it so it would look more like Google+.