Exodus is a program that has a simple interface, that has been developed to be used with the Jabber instant messaging service, but that can be used for the MSN, ICQ, Yahoo! and AIM networks.
Despite the simple appearance of the application, many of the functions are somewhat hidden and can be unpractical for those users that are used to other more simple programs.
Unlike other similar clients, this program doesn't include a conversation manager, nor an address book in proper conditions to be able to classify our contacts very easily.
If you're looking for an instant messaging client that's compatible with several of the most used services, try out Exodus, it has the added bonus of being a lightweight application.