RE: CRM's user chat mechanism
The social pane inside of CRM does this. It works much like a Facebook relating to the Opportunity or Account they're working on. There's even a generic dashboard where they can see conversations about all of the Opps/Accounts they own or follow.
Beyond that, there's also a Yammer integration, but I don't remember if that works on premises, or just online.
Lastly, Microsoft's new Teams tool that is replacing Skype for Business sometime in the next year has the ability to pull from CRM into chats, which can be very useful. But I believe that is online-only as well.