Network and addresses
IPv6
Next-generation addresses: plentiful and often free as a whole subnet.
IPv6 is the new address format (like 2001:db8::1). There are practically endless addresses, so providers often give them for free, sometimes a whole subnet.
IPv6 helps for a mail server, a VPN and access from mobile networks where IPv4 is shared. But it cannot fully replace IPv4 yet — a site needs both.