Openfire

1) set up an external DNS entry so that people can find it.

2) configure your firewall and networking to allow the correct access from the external network to the internal IP/ports of your openfire server

3) set up the clients to properly connect to the server.

https://community.igniterealtime.org/thread/47660

http://www.experts-exchange.com/Networking/Protocols/Q_25698311.html

I don't know penguin, but I am guessing it is a valid XMPP messaging client with the proper features.