Psi is the premiere Instant Messaging application designed for Microsoft Windows, Apple Mac OS X and GNU/Linux. Built upon an open protocol named Jabber, this is a fast and lightweight messaging client that utilizes the best in open source technologies. Psi is able to interoperate with other, proprietory messaging systems such as AOL's ICQ and Microsoft's Messenger. You can keep in contact with your friends, regardless of whether they use AIM, ICQ, MSNM or YahooM. It's even possible to use Internet Relay Chat!