calendar event reply-all

I guess that is one way.

If you still have the original invite email, you can reply all to that, but if the attendee list has changed then that is not much use.

If your calendar is synced, you could use the web interface for your calendar provider, or if your calendar synced with multiple devices, use one of those to email the attendees.

This seems basic and should be included

+1 this should be added. Please consider it. This is very important one.

+1  Please add Reply All and Forward options,