One free NAS distribution that I hadn't thought of in a while is the one from Turnkey Linux. When thinking of purpose-built NAS server software that is free, the three that usually come to mind nowadays are FreeNAS, Openmediavault and Openfiler. While these are all great NAS software distros, one other one that is readily available and kept up to date is Turnkey Linux server edition.
The Turnkey Linux appliance is described:
Simple Network Attached Storage
An easy to use file server that combines Windows-compatible network file sharing with an advanced web based file manager and includes support for SMB, SFTP and rsync file transfer protocols. The server is configured to allow server users to manage files in private or public storage. Based on Samba and eXtplorer.
Turnkey Linux File Server Appliance is, of course, built on the framework of Turnkey Core which is based on Ubuntu Linux. As with all Turnkey Linux appliances, the file server can be installed in several different ways:
Build formats: deploys on bare metal, virtual machines (e.g., VMWare, VirtualBox, KVM, Xen) and in the cloud
The appliance comes with Webmin for easy web-based configuration and has SAMBA installed for easy sharing of files with Windows computers.