1) This link is the finished source code for the askeet project. Unfortunately, the askeet project is notorious for being filled with bugs. Furthermore, this is based on a much older version of Symfony and will quite possible have problems with the current version of Symfony.
2) If the script did work, then yes, it would function like any other Symfony web app (including the sandbox) and could be made to work on a domain like http://www.askeet.com/
3) There are always 2 parts to a Symfony project. The first is the project itself - both the sandbox and the askeet projects are examples of that. The second is the symfony library upon which the projects rely. These can either be placed externally to the project or right inside the project itself (as is the case with sandbox). In either case, the config/config.php file needs to point to the location of the library.
4) The link you have for askeet is the closest thing to a working script that exists (that I know of). Askeet isn't meant to be an application you download and use. Rather, it's intended to be a learning tool, and the source code was created to assist you as you are building along with Symfony.