Alt-F provides a free alternative firmware for the DLINK DNS-320/320L/321/323/325

Alt-F has Samba and NFS; supports ext2/3/4, VFAT, NTFS and ISO9660 filesystems; RAID 0, 1, 5 (with external USB disk) and JBD; supports 2/3/4TB disks; rsync, ftp, sftp, ftps, ssh, lpd, DNS and DHCP servers, DDNS, fan and leds control, clean power up and down... and more.

Alt-F also has a set of comprehensive administering web pages, you don't need to use the command line to configure it (screenshots).

Besides the builtin software, Alt-F also supports additional packages on disk, including ffp packages, that you can install, update and uninstall using  the administering web pages.

Alt-F is still beta and is being developed and tested on a DNS-323-rev-B1, a DNS325-rev-A1 and a DNS-320L-rev-A1 hardware boards. Other models and boards are said to work.

February 3, 2015: Alt-F-0.1RC4.1 has been released