There are a few multi-protocol chat clients — some common ones include Apple’s official Messages app and Adium for OS X, as well as the popular cross-platform Pidgin. I have opted out of using these multi-protocol chat clients for the most part: chat protocols often become outdated and re-implemented, and usually official dedicated clients that are far superior. Furthermore, many chat services have migrated to having a web-based interface, such as Skype (amidst many others). Many users now just open their chat clients as a separate tab in their web browser.
All-in-One Messenger is a Chrome app that essentially does the tabbed browser approach — it a tabbified, multi-protocol chat client, that behind the scenes more or less interfaces with the web clients available for the number chat services. However, it provides an intuitive interface that is streamlined for switching between chat protocol tabs in a way that is not provided by the tabbed browser view nor through having each of the individual apps running separately.