Viber is a cross platform application. Initially only for mobiles, but today they have finally released a PC version!

Programs like Viber and WhatsApp are better than Skype in that they automatically use one's phone number as a username. That means there's no need to register yet another username. They are also designed as background processes. Thus ensuring you'll find a lot more of your contacts there.

You might call it a Skype killer, but only the PC version currently enables video chat.

Anyway, it deserves a portable version, even if for nothing else than showing support for such an unlikely move in the current mobile-only sentiments of new developers.