Find me something that competes with the features and enterprise support of Exchange, Office, Lync, Sharepoint, Outlook ... that runs on Linux.
Unfortunately, I don't know any of these utilties except "Office" which is easily replaced by LibreOffice. The fact that I don't know them lies in the nature that don't solve anything of value for me. Maybe I am working differently from others. Instead of telling me product names, tell me what you do (I also don't want to know what you do with the products; it is wrong to describe your problems by providing me wrong approaches for solutions). There are plenty of solutions that can be used and you can also develop some for yourself for your special purpose.
What I need more is a reasonable terminal application, Xmonad as a desktop (UTF-8 support), easy integration of gnupg into a mailclient, I need ssh, tmux, text-based vim, a text-based IRC client, a full compiler suite which is ready-to-use. I also need inspection tools for all my system components. And I need a reasonable way to manage time (UTC), so when I travel around the world, I just setup the timezone and not the time itself.
And now tell me, I should install CygWin, because I don't know this poorly emulated Windows crapability layer.