Are you going, maybe? No! Well tell them, it's easy

Everyone invited (including the manager!) to an event can set their attendance to one of three options, I can make it, I might make it, I can’t make it. Whichever option is selected, a message (excuse!) can be left, which all attendees/invitees can read.

If the event is public then anyone who finds the event can set attendance so the event manager knows who and how many to expect.

The manager of the event receives an email whenever attendance is set; and event attendance can be reviewed simply either on the event detail page; or if a community event via the event listing page.