It's a theme and an alternate admin area. From the code on github[1], it looks like you drop the theme[2] in as normal (in `wp-content/themes`). Then you put the `wp-svbtle` directory in the same directory as your wordpress install.

Doesn't really replace the built in WordPress admin area, just adds another one.

1. https://github.com/gravityonmars/wp-svbtle 2. https://github.com/gravityonmars/wp-svbtle/tree/master/wp-co...

It's both.