Microsoft sure has a lot of warts, but even as a Linux enthusiast, I cannot deny that Outlook "Just Works" with a frankly shocking set of basic stuff. Login for the first time, check your email, hey there's your meeting with your manager on your calendar, and now we can add new events just by putting you in this group, etc etc. There's dozens of little integrations baked in here that a tech enthusiast could feasibly replace in isolation, all of which vanish the moment you turn off the Exchange server or whatever it is. It's way more complex under the hood than most people realize, which is why "ditching Microsoft" so often turns into "Adopting Google Apps", as they have a similar turnkey solution to most of the same problems.
Not meaning to be a big ball of negativity, but as I haven't really explored here... in the FOSS space, what is the equivalent? Which tools are the most polished, and what server backends could be hosted on-prem to gain the same basic integrations with login, email, calendar, chat, and video conferencing?