[bluetidepro]

Slightly off topic, but do you know what I want? A calendar app that allows me to add events that don't have an end time. Sometimes I know when things will start, but don't care/know when it will end. Let me make the end time optional, and then just give me the alert when something happens. It's not like you get an alert when it ends. I don't get why any single calendar app I've ever used won't do this.

[autarch]

On Google Calendar, you can make events that are 0 minutes long. That'll give you an alert when it starts.

[girmad]

Many apps let you set 'reminders', which are effectively what you describe.