Taken from Nas4Free.org:
NAS4Free is an embedded Open Source Storage NAS (Network-Attached Storage) distribution based on FreeBSD. This project is a continuation of FreeNAS 7 series project.
As you will be able to see NAS4Free uses a web interface similar to the one that FreeNAS used to use, the previous interface was much better(my opinion). The download is quite small at around 50MB(compressed archive) you will need 7zip to decompress the archive.