If you have logged into Office 365 email lately, you may have noticed there is an additional button along the top bar. This is the web client for Skype for business (SFB) that is built into Exchange Online's OWA client, not to be mistaken for the Skype Meetings web app. It is especially useful when logged into a kiosk or device without access to the SFB client, and is more lightweight, less intrusive and more intuitive to me than the full-fledged client. Functionality is limited: It excludes access to video chats, you cannot add SFB belonging to another tenant or external Skype users to your contacts - these are some of the features that are removed.
It also requires you to have access to Outlook Web Access (OWA) through Exchange Online. This service is not available to you if you have not migrated your mail to Exchange Online, or if you have purchased SFB licenses as a standalone product. Myself, my mailbox is still on-premise, and will remain so while some of my users remain on-premise in order that I may support them. (some features of exchange are inaccessible if you do not have an on-premise mailbox, such as the on-premise ECP and all it's features).
Nevertheless I use the web app through a loophole: I log in through the Exchange Control Panel (https://outlook.office365.com/ecp/) which I have access through by being assigned an admin role on Exchange Online. Still, it would be nice if the Skype for Business web client was extended as a stand-alone service instead of being tacked on to OWA.