Miranda IM is a multi protocol Open Source messenger client that embeds into a simple user interface some advanced features for which you don’t have to pay a thing. The latest version is portable, thus it requires no installation and runs low on system resources. With over 350 plug-in, this messenger recommends itself as a powerful contender for other mainstream solutions. And it does that by offering support for all of them, starting with AIM and ending with Yahoo.
Over 20 add-ons are there ready to help you integrate Facebook or Skype, add several languages and block annoying spam messages.