Alt-F is a free and open source alternative firmware for the DLINK DNS-320/320L/321/323/325/327L and DNR-322L.
Alt-F has Samba and NFS; supports ext2/3/4, BTRFS, VFAT, NTFS and ISO9660 filesystems; RAID 0, 1, 5 (with external USB disk) and JBD; supports up to 8TB 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 its own, ffp and Entware-ng packages, that you can install, update and uninstall using the administering web pages. Debian can also be installed under Alt-F but has to be used from the command line.
Alt-F is being developed and tested on a DNS-323-rev-A1/B1, a DNS325-rev-A1, a DNS-320L-rev-A1 and on a DNS-327L-rev-A1 hardware boards. Other models and boards are said to work.