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/