Luma is an event, calendar, and ticketing platform.
Luma makes it very easy to RSVP for free events online or in person, without having to go through a long sign up process.
It has very complete email update and notification features. By default, it will send an email the day before and then the hour before an events start time, but can be customized.
For shared, curated calendars, you can also send newsletters to all those that are subscribed to the calendar.
It is a proprietary platform, but it does have an API and can be embedded as both individual events or entire calendars. I think of it mostly as like a "Substack for Events". I can export the email addresses of attendees and import them elsewhere.
I've asked the team to add an option to map domains to calendars – so I could do calendar.example.com – as another way to not just send links to someone else's platform.
Examples of Calendars
Fission calendar: https://lu.ma/fission, as well as embedded at https://fission.codes/events>
DWebYVR calendar: https://lu.ma/dwebyvr, as well as embedded at https://dwebyvr.org/wiki/Calendar
Alternatives
I have used Tito for many years for both no-charge and ticketed events.