Skype is voice chat;
ICQ is the biggest chat tool; AIM is a chat tool after ICQ.
IMVU is a 3D character scene chat tool.
Yahoo Messager should be the fourth largest chat tool, second only to ICQ, AIM and MSN.
Facebook and Twitter are the most popular social tools at present, just like Renren in China and Weibo.
There should be other chat tools, but the proportion is relatively small.