If you have friends on all of the instant messaging services, Miranda will make your life much simpler. With support for MSN Messenger, ICQ, AIM, Jabber and Yahoo and all versions of Windows.
Miranda is also very small and can even fit onto a floppy disk. Extra services can be added to the software as they become available.
All of the contacts are merged into one list. There are different status icons for users on the different services so you can quickly see who is online.
Although it consolidates all of your instant messaging friends, it does not support some of the advanced features.