Biscuit is a single-page responsive Jekyll theme. This is the most simple and still-good-looking Jekyll theme that you can find.
You can use this theme with Jekyll or you can simply use it with Github Pages. For local usage just download Jekyll, use installation guide for more. You can download latest Biscuit from its Github repository.
If you prefer to use Github Pages, you do not need to download it, upload files to a new repository...etc, just fork and use it.