AOL AIM ICQ and GTALK all-in-one

AOL/AIM and ICQ are in the same company now, and the accounts can
communicate with each other. Google Gtalk allows a AOL/AIM/ICQ to
login as the same time.

Yahoo Messenger and MSN can talk to each other too. Now you can choose
two clients and cover four Instant Messengers.

In china Tencent QQ does not allow cross platform communication, it
was a clone of ICQ but now QQ is the most powerful and crowed IM in
this planet.