How do I turn the echo service on in Snow Leopard? I'd like to temporarily turn on the echo service (TCP and UDP port 7) on in Mac OS 10.6 (Snow Leopard).  I guess this involves using the launchctl/launchd?
Port number 7 is traditionally labeled "echo", but AFAIK no modern OS implements it.

Note that this is completely different from the ICMP_ECHO used by ping.  That is enabled by default, although it will be blocked if the firewall is placed in stealth mode.