Skype for Business client (former Lync client)
Do you already use Outlook? Then you already have a Skype for Business Client in your Microsoft Office package.
If you do not have a Microsoft Office package, you can install the standalone client. Here you will find detailed instructions for Windows. For MacOS you can download the client here.
Unfortunately there is no fully featured Skype for Business client for Linux.
Presence and chat in Skype for Business client
Skype for Business also for smartphones and mobile devices?
Yes, you can also download and use the Skype for Business Client on your iPhone/iPad or Android device from the respective App Store.