What are some alternatives?
When comparing ApPHP Calendar and Microsoft Hotmail, you can also consider the following products
Google Calendar - Spend less time managing your day & more time enjoying it
Calogic - CaLogic is a feature rich, muti-user, open source web calendar.
Teamweek - A project management software to help you get the best overview. Plan fast, change plans faster!
CalendarX - Get a calendar your audience can follow
Apple Calendar - Calendar is a personal calendar app made by Apple Inc. that runs on both the macOS desktop operating system and the iOS mobile operating system.
Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.