The Skype for Business App SDK was announced at Build 2016 a couple of months ago, but it's only now available for download. So developers of both Android and iOS apps can finally start working on integrating Skype's messaging, audio calling, and video calling into their own apps.
The first leg of this initial SDK release is "remote advisor," a solution that lets app developers enable the "guest meeting join" capability to let guests start communicating with companies that already have a Skype for Business Server and an active Skype for Business Online service. In other simpler words, companies that are already using Skype for Business can now update their mobile apps to give their users and customers the option to talk to them via said apps.
One of the examples given during Build 2016 was MDLIVE, a telehealth provider that is working on letting patients get in touch with health experts instantly through its mobile app. You can read more about the purpose of the SDK and download it at the source links below.