Hello Firas,
I've not been involved with the project for many years, but maybe I can help you. It looks like the source was migrated from google projects to github recently (I think google projects is being shut down).
On the github page, there is a "code" tab next to "issues". After clicking the code tab, you can either download the source as a Zip file or pull it through git.
I hope that helps! I won't be able to answer any questions related to the contents of the source or NERO, given how out of date I am with the project.
- John