Calendarsnack is a service that allows users to send calendar invites to email lists directly from their calendar client. It includes prebuilt landing pages, RSVP buttons, and a VIP email list. When events are created, updated, or cancelled in the user's calendar client registered with Calendarsnack, the service automatically sends updates to recipients of the calendar invites. Calendarsnack takes calendar event data from the user's client and distributes it as invites, tracking RSVPs and updating recipients when events change.