Tcpdump
http://www.tcpdump.org/

Wireshark
http://www.wireshark.org/

NS-2
http://www.isi.edu/nsnam/ns/

XMPP
http://xmpp.org/

Ejabberd
https://www.ejabberd.im/

OpenFire
http://www.igniterealtime.org/projects/openfire/

Pidgin
http://pidgin.im/

Rsync
http://rsync.samba.org/