As far as I know, there is simply no alternative for Business Calendar. The way you can work with profiles and customize the UI is something I never found in an open source calendar app. Apart from that, I've found Simple Calendar (now Fossy Calendar) and Etar to be extremely buggy.
It doesn't need a network permission to work properly, so the trackers stay dormant.
Handy tip: I purchased Business Calendar v1.x Pro years ago and the Pro features in Business Calendar v2.50.3 can still be used by simply installing the v1.x Pro APK (you can even disable it). No need for Google Play. Newer versions (with all the Microsoft account bullshit implemented) do not allow the use of Pro features this way anymore.