nmap
Nmap 3.70 released -> http://www.insecure.org/
this simple command allows to know which local hosts are up:
nmap -sP <masked IP network> (ex: nmap -sP 192.168.1.0/24 )
This friendly scanning can be added to the crontab, allowing a daily report of the open ports:
nmap -sT -P0 -sV <host> 2>&1 | mail -b <your mail> \ -s "[nmap] `date -I` scan report" <host_owner_mail>
For IPv6:
nmap -sT -6 -P0 -sV <host|ipv6>