Dynamic DNS support through many providers. Firewall configuration. Auto blocking of failed logins. That last one is great, especially if this device will have a public IP address.
Management and monitoring via SSH or Telnet, plus SNMP.
Network backup via custom system or rsync
Network settings, including hostname and IP address settings. It can also do IPv6 tunneling.
DSM, DiskStation Manager, is the software you’ve been looking at. This applet sets its settings, including the login screen background and on what ports the DSM is served.
Regional settings for time and language
Notifications via email or SMS when bad things happen on the NAS
Power and UPS settings, including HDD hibernation for power consumption minimization