From Erik Hinterbichler:
Gabble is a native Mac OS X desktop client for the Yammer messaging service. It's the first Yammer desktop client designed specifically for the world's best operating system. Let Windows users wrestle with that crazy Adobe Air stuff. For Mac users there's now a better way.
Gabble is written in Cocoa and Objective-C 2.0, which means it's a first class citizen of your desktop and behaves the way you expect it to. So you can spend less time frustrated by annoying UI inconsistencies and more time enjoying the social media revolution.