YammerYour company's private social network
What is Yammer?
Part of Microsoft 365, Yammer is a social network just for your company, though you can invite people from other companies to participate in discussions.
Think of it as Facebook for your business.
You can post status updates, have discussions, share files, create groups and send private messages.
Host live or on demand video events with everyone across the company, anywhere in the world, and on any device, to communicate news and updates.
Yammer is primarily designed for large companies, where finding the right staff member and communicating with disparate colleagues can be difficult. The service can be useful for disseminating news and encouraging discussion in smaller businesses, too.
There are apps for Windows and Mac which you can download from here. (For Windows you would usually want the 64-bit version.)