Yesterday Paul M Jones tagged the beta5 for the system repo.

So you can download the system from http://auraphp.com/system/downloads/

via composer

Creating aura framework based projects has been made easy with composer. You can run

php composer.phar create-project -s dev aura/system your-directory

What it does is almost similar to git clone and installing via git as below

via git

git clone https://github.com/auraphp/system
cd system
php update.php

you can also skip php update.php with

php composer.phar install

You can read some basic introduction from http://auraphp.com/system/

NB : If you haven't heard about composer you can read it from getcomposer.org