My take on the systemd unit for the Debian Jessie platform. Requires a nodebb user set up and NodeBB installed to /var/nodebb:

[Unit]
Description=NodeBB forum for Node.js.
Documentation=http://nodebb.readthedocs.io/en/latest/
After=system.slice multi-user.target

[Service]
Type=simple
User=nodebb

StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=nodebb

Environment=NODE_ENV=production
WorkingDirectory=/var/nodebb
ExecStart=/usr/bin/node loader.js --no-daemon --no-silent
Restart=always

[Install]
Alias=forum
WantedBy=multi-user.target

Enable with sudo systemctl enable nodebb.service and start with sudo systemctl start nodebb.service.
Thanks to @Apxukoc and @julian for the original unit and tips.