Alt-F provides an alternative firmware for the DLINK DNS-323 and DNS-321, that can be either run "on top" of the vendor firmware, or flashed into the hardware.
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; greater than 2.2TB 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.
It is also easy to install, just copy two files to your disk and reboot; on the second reboot you will be back to the usual vendor software (instructions). Or just use the vendor's firmware upgrade page to directly flash it.
Alt-F is still beta and is being developed and tested on a rev-B1 hardware board. rev-A1 and rev-C1 boards are said to work.