Mac OS X comes with iMessage, Apple’s messaging system, which is also built into iOS. While iMessage is great, it doesn’t allow you to exchange messages across platforms. Sign in to Viber: an app for Windows, Mac and Linux that does just that.

Viber is free software that performs two key functions. There is a text chat, very similar to SMS messaging, but with the ability to send images. Then there is the voice call; Viber boasts high definition audio for superior quality and clarity.

In addition to iMessage and Viber, there are many messaging apps; Skype covers the same market and has a huge reach. However, Viber allows users to transfer a call from one device to another, an excellent feature that its competitors inexplicably lack.

Other benefits include:

• Easily connect to Viber using your existing phone number, making signing up super easy.
• A series of graphics called “Stickers” that you can send to your contacts for free.
• Full multi-device support for Windows, Mac and Linux (Ubuntu).
• Free calls and messages to any country in the world.
• Mobile apps to keep the conversation going on the go.

With Wi-Fi and 3G support and an ad-free interface, Viber is rapidly gaining momentum. For calls to regular phones, try the ViberOut additional service.