This is a chat room example from Erlang/OTP R11B documentation.
It is executable totally.
The step comes follows if you want to hack it:

• compile the messenger.erl(c(mesenger).), and copy the messenger.beam to all of the nodes you own
• choose one node as your chat room server, type command messenger:start_svr().
• type the command messenger:logon(node_a). on the other nodes to login
• if you want to send message to node_b, type messenger:message(node_b, "Hi node b, how are you").
• if you want to log off, just type messenger:logoff().
• Remeber that you have to put the same .erlang.cookie file in all of the nodes above, it have to be put into your home directory.

Happy hack.