Portable Software: Pidgin (Instant Messenger)

Pidgin Portable (formerly Gaim Portable) is the versatile instant messaging client packaged as a portable app, so you can take your IM settings and buddy lists with you. It has all the same great features as Pidgin, including support for AOL, Yahoo, MSN, ICQ and Jabber networks, but there's nothing to install on the local PC. You can also easily add portable encryption plugins for secure, encrypted messaging.

You can log into multiple networks all with the same program. All your IM settings and buddy lists are self-contained, so it leaves no personal information behind on the machine you run it on.