Yammer does the job!

Like any social platform, Yammer has its nuances. But its very intuitive and people come up to speed with it in no time. Its similar enough to Facebook that people easily "get" it. Groups are easily created to focus attention and discussion around projects or events that matter. A key feature is the ability to add branched replies to comments or events that have already happened. Its not only a linear stream of consciousness. This enables context around a topic.
Glad to see that Microsoft is continuing to build new features into the platform. Keep it moving!

morlan9119 about Viva Engage, v6.6.20