Sending invitations
You can invite other people to any event on your calendar simply by adding their email addresses in the Guests section of the event.

Guest RSVPs
Guests can RSVP to your invitations by email, whether or not they use Google Calendar themselves.

Guest comments
Comments submitted by your guests are displayed for all your invitees to see.

Event reminders
Reminders help you keep track of important events. You can choose to be notified by email, popup window or text messages sent right to your mobile phone.