The list is very big and every service provider has their own chat messenger application: Google has GTalk, Yahoo has Yahoo Messenger, Windows Live has Windows Live Messenger, etc. People have their contacts on different mail networks like Gmail, Yahoo, Windows Live, Facebook, AOL, etc.
We know that Windows messengers are not as popular as mobile IM apps, but there are also some great ones. However, what if you are looking for an instant messenger for your Windows computer or Mac? As developers are getting crazy about instant messaging function for mobile devices, we can see so many IM apps provided for your Android/iPhone. The integration of instant messenger and popular online services has reduced the need for an IM client, especially when comes to a PC platform, but it hasn't vanished completely. 10 Best Instant Chat Messenger Alternatives for PC/Mac